Showing posts with label Auto. Show all posts
Showing posts with label Auto. Show all posts

MPH to FPS: Mental Calculation of Miles per Hour to Feet per Second

How to Instantly Convert MPH to FPS When Driving

- The Quick and Easy Math Trick -

Simply divide miles-per-hour by 2, then multiply the result by 3 to find feet-per-second.

This is the easy, quick math way and gives a fairly accurate answer. Your answer will be accurate within 5%. As an example, 100 mph converts to 150 fps. If one does the more complicated method of math calculation (detailed further down the page), the resulting answer would be 147 fps.

"How many feet per second..." is a math question usually relating to cars and driving.

Easy Table Conversion from MPH to FPS Examples Chart


The More Difficult (and More Accurate) Answer

To prove the quick math shortcut calculation works:
  1. First. convert MPH (miles-per-hour) to MPM (miles-per-minute) by dividing MPH by 60.
  2. Then convert miles to feet. There are 5,280 feet in one mile, so multiply MPM by 5,280 to get FPM (feet-per-minute).
  3. Lastly, convert FPM to FPS (feet-per-second) by dividing by 60.

Examples of the Longhand Math Converting Miles-per-Hour (MPH) to Feet-per-Second (FPS)

Math Example One

You're going 25 mph. How many feet is that per second?
  1. Conversion from mph to fps is as follows: If we divide by 60, we get miles-per-minute: 25/60 = .416667.
  2. For accuracy's sake, now is a good time to convert miles to feet. There are 5,280 feet in a mile so we multiply mpm times 5,280 to get feet-per-minute: 416667 x 5280 = ~2199.99 feet-per-minute [note: "~" means approximate].
  3. To convert from feet-per-minute to feet-per-second, we divide the answer by 60: 2199.99/60 = ~36.667 feet-per second.
  4. This answer is within 5% of the one you get doing the easy math, which says 25 mph equals 37.5 fps.

Math Example Two

65 mph. How many feet per second?
  1. Conversion from mph to fps is as follows: If we divide by 60, we get miles-per-minute: 65/60 = 1.0843333333333.This makes sense. After all, 60 miles an hour is obviously equal to a mile-a-minute.
  2. For accuracy's sake, now is a good time to convert miles to feet. There are 5,280 feet in a mile, so we multiply the miles-per-minute times 5,280 to get feet-per-minute: 1.0843333333333 x 5280 = ~5725.28 feet-per-minute.
  3. To convert from feet-per-minute to feet-per-second, we divide the answer by 60: 5725.28/60 = ~95.421 feet-per second, which is the answer.
  4. This coincides within 5% of the table above, which says 65 mph equals 97.5 fps. 

Math Example Three

120 mph is how many feet per second? Conversion from mph to fps is as follows.
  1. If we divide by 60, we get miles-per-minute: 120/60 = 2.000. This again makes sense. After all, 60 miles an hour is a the usual mile-a-minute. So 120 mph would be 2-miles-a-minute.
  2. To convert miles to feet. There are 5,280 feet in a mile, so we multiply the miles-per-minute times 5,280 to get feet-per-minute: 2 x 5280 = ~10560 feet-per-minute.
  3. To convert from feet-per-minute to feet-per-second, we divide the answer by 60: 10560/60 = ~176 feet-per second.
  4. This number is within 5% of the table above which says 120 mph equals 180 fps.


Quick way to find reverse, i.e., convert from feet-per-second to miles-per hour: divide fps by 3 and then multiply by 2 for mph.

Easy Table Conversion from FPS to MPH Examples Chart


Doing 20 Miles-per-Hour? That Is 30 Feet-per-Second.

The laws of physics seldom take a vacation.
Most of these cars would not be able to stop in time

And for Your Amusement,
the Most Ridiculous Car Chase Ever.

How to and the Process of Getting a Car Loan

How to get the best rate for an auto loan, plus a couple important tips and tricks for buying a new or used car.

And as for getting a car loan when you have bad credit or no credit or no job, here is probably the most important tip of all...
  • The larger the down payment you are willing to make, the more inclined the bank or other financial institution will be to give you the loan.

Both new and used car sales continue to fluctuate, and so the demand for car loans does the same. As demand fluctuates, so do the shenanigans and other nonsense by dealership finance departments and other lenders. This page will provide you with what you need to know about getting the best possible rate on your auto loan. Failing that, it will at least keep you from getting the worst.

Auto Loan Guide - Things to Do and Not Do

Clean Up Those Credit Reports

First thing you need to do is get copies of your credit reports. You are entitled to one free report a year from each of the three major reporting agencies. The most legitimate website to get them from is They will make you work for it by subjecting you to a bunch of sales pitches for their non-free products, but this is the site most consumer groups and others recommend.

Review your reports. If you find any errors negatively impacting your credit score, you will have to jump through whatever hoops are necessary to get them fixed. Most loan officers don't even seriously bother to look at the reports; they just look at the credit score. Have the wrong credit score and you may not even be able to get an auto loan. Have an unfairly low credit score, and you will be paying hundreds and possibly even thousands more in interest over the course of your car loan, not to mention being subjected to higher monthly payments.

It is imperative your credit score be as high as possible. One doesn't have to be a rocket surgeon to know the higher your credit score, the lower the interest rate on your auto loan will be. In fact, reading this Credit Score Guide for Beginners would probably be a good idea.

Avoid Auto Dealer Financing

Epic Fail!
Don't do this!
Car dealerships and used car lots are the absolutely worst place to get an auto loan.

Seriously, you might as well go to one of those loan shark outfits you see at the mini-malls. The auto dealers will use every trick in the book against you. They make as much or more money on the financing as they do on the car sale, itself. More often than not, whatever interest rate is initially promised invariably runs into a "problem"; and they will insist they can only do the financing at the higher interest rate and higher monthly payments. It's even been reported they will sometimes pull this stunt when the car is already sitting in your driveway.

As a side note, by all means ask about their zero financing they constantly advertise. Problem is, somehow nobody every seems to qualify for it... If you do happen to be one of the lucky few, well and good. But don't count on it.

And while we're at it... When you have decided to visit a particular dealership or used car lot, it wouldn't hurt to first check them out at RipOffReport and the BBB.

Best Way to Get a Car Loan Is from Your Current Financial Institution

Do you feel lucky?
With any luck, your financial institution has already been poking you with a stick;
trying to entice you to get an auto loan with them.

Your first resource should be your existing bank or credit union. Presumably you have been with them for awhile and are considered to be a good customer. What you would really like to accomplish is to get a pre-approved auto loan from them; succeed and your problem is solved.

Do not mention your pre-approved loan to the car dealer prior to closing the deal on your car purchase price. Otherwise they will raise the car price to offset the money they are not going to make from the financing.

If your financial institution seems somewhat reluctant about the pre-approval idea, don't push it. Stay lovable and don't burn that bridge just yet. Ask about and pave the way to apply for an auto loan with them after you have negotiated the price for the car.

Getting a Car Loan from Other Than Your Existing Financial Institution

The Shopping Around Process

Did your existing financial institution fail to come through? Fine; once you've got the car situation taken care of, your next project will be to find a better place to do your banking business.

Give your regards. Select "auto" from the menu at the top of the screen. Use their search feature to see what the best auto loan rates and conditions are, etc. Don't actually make an application just yet.

Check out your local banks and credit unions. Visit their websites. See what their rates, fees, and conditions are. Again, don't actually apply.

There are also some worthy exclusively-internet entities out there who do car loans. Just be sure to research them first. You do not want to get tangled up with the wrong one.

Network! By all means ask friends, neighbors, co-workers, etc. for recommendations as to where to get the best car loan. Applying for an auto loan at a place where you can use an existing good customer as a reference certainly won't hurt.

Also be attuned to what people say about auto loan places to avoid.

How to Apply for the Car Loan
This is all a pain in the neck.
But even a 1% loan rate savings can add up to a significant amount of money over time.

The Application Applying Process

Well, you've cleaned up your credit report and have done your research. Time to apply for the loan.

Pick and rank your best five candidates from your research. Work your way down the list. Make it known you are shopping for the best rate; this accomplishes three purposes:
  • You are implying you have no concerns about being accepted for the loan, your only concerns are as to terms. Appearing confident favorably affects perception.
  • You will not appear desperate or sneaky when it is noted you are making multiply inquiries.
  • Induces competition and a sense of urgency as to interest rate offered and quickness of response.
In some cases you will have the option to apply in person or via their website. Put some thought into what would work best for you in that particular situation.

Do make all your applications within a 30-day time frame. Multiple loan application inquires will reduce your credit score. But if you make all your duplicate applications within a 30-day period, it is supposed to be categorized as only one inquiry by the credit reporting agencies.


The above information should work equally well as to getting the best motorcycle, truck, boat, or even airplane loan rates. However, if the boat or airplane is over a 100K, then you can probably afford to get a financial adviser involved. Preferably one with lending institution connections.

Yes, getting the best auto, truck, or SUV loan rates can be a lot of work and a pain in general. The more effort you put in to it, the more money you can save. One thing you can do is to make the project an iterative process, i.e., don't try to do it all at once. Just do one or two aspects a day. It will be done before you know it.

Just a Couple Car Buying Quick Tips
Thrown in for Good Measure

New Car Buying Tip

There are reports saying buyers can get a better price through the website than through going to the car lot. There may even be a choice of websites, i.e., manufacturer website vs. dealership website.

Every manufacturer does things their own way. As an example, the manufacturer website may simply refer you to the appropriate dealership website. Or not. Things are always changing.

It should also be noted more and more dealerships are directly owned by the manufacturer.

Used Car Buying Tip

When a dealership takes a car in trade-in, generally one of two things will happen to it.
  • If the dealership thinks it is a good car which will outlast their warranty program, they will give it a tune-up, detail it, and put it in their used car section.
  • If they don't think it's such a good car, they'll sell it off at a wholesalers' auction and it ends up in some used car lot.

What is the significance of this to the used car buyer?
  • The better cared for, more reliable cars are to be found in dealership used car sections.
  • The more tired, riskier cars are generally at places exclusively selling used cars.

Auto Safe Driving Tips - How to Control a Panic Stop and Avoid a Collision

Here is how to avoid rear-ending the car in front of you when the emergency panic stop is "too late". A true story. Happened over a decade ago.

Preventing Panic Stop Collisions - It Can Be Done

The 82 Camaro That Lived to Tell the Tale

Am doing the speed limit in downtown traffic. Needed to get gas. I squint at the Food Mart gas prices sign across the street on the left. Why do they make the numbers so small? All the other places have normal-sized numbers. I squint and squint…

Suddenly an ambulance siren goes off. I jerk my eyes to the front. All the traffic had stopped dead in front of me because an ambulance coming from the opposite direction had been using its red lights without the siren. And when I say stopped dead in front of me, I mean up close and personal. It was all over.

I slam on the brakes. Way too late. Less than four seconds to impact. My car and the poor guy's car in front of me are about to get totaled. Time really does slow to a standstill…

And then I remembered an article I had read a long time ago.

I turn the steering wheel to the right towards the curb. The car actually goes where I tell it to go. That's right, whether ABS or solidly locked wheels; where you tell the car to go, the car will go.

My car is no longer aimed at the reprieved guy in front of me. I finally come to a stop beside the other guy's car and short of the curb. Had to backup to get back into the lane. A very lucky, happy ending.

Car Traffic Safety Tip #1 If something that is not in front of you is too hard to see, don't even try. You never know what suddenly might be happening in front of you.

Car Traffic Safety Tip #2 Even when the wheels are locked, your car will still go where you tell it to go,  All you need is the presence of mind to turn that steering wheel.

Innate Response and Never Just Give Up

While writing the first, another story came to mind. This one happened over three decades ago.

A road very similar to this one, but still slick from the rain; good thing that tanker truck wasn't around.

Booming down the hill on a country highway. Doing 60. Am even at legal speed.The rain had finally stopped.

Someone waiting in a white pickup truck suddenly floors it from a cross-street on the right; loses control, spins around, and stalls.

There he sits. Right in front of me. 60 mph, two seconds to impact...

Hard right. Hard left. Coasted for the next half mile, recovering from the near miss.

It was an innate response. At 60 mph and at that distance, one just knows when there is not even time to hit the brakes. Cars are designed not to flip. So at least try to steer your way out of it. After all, you have nothing to lose.

Car Traffic Safety Tip #3 It's not over 'til it's over. Keep trying until it is.

Some Final Thoughts

In both of the above situations, given the speeds and distances involved; my automatic, first response was exactly what most people would have done. We seem to be genetically programmed to automatically respond with the correct, initial reaction in such situations. Unfortunately, life being what it is, that first initial reaction is not enough.

In both situations, a second action was required to save the day. Unfortunately, that action is not genetically programmed into us. It is something which has to be learned, which you have indeed now done.

In the first incident, most people would have rammed into the car; not knowing that simply turning the steering wheel could have saved the situation.

In the second incident, after making that first hard right turn, most people would have then run off the road; hitting whatever was around to be hit, or even worse, going off some version of a cliff or deep ravine. In fact, this seems to be a case where our genetic programming actually works against us. After the first reaction, most people then tend to freeze, i.e., mentally withdrawing from what is happening. One has to make the deliberate, conscious decision to "stay in the game". It's not over 'til it's over.

Take care.

Controlling Emergency Panic Stops and Avoiding Collisions

Miles per Gallon and Cost per Mile Formulas

How to Calculate Miles per Gallon and Cost per Mile Using Formula Template

For folks who want accurate miles-per-gallon and cost-per-mile answers.

For quick, easy answers; simply use the MPG and CPM formula templates and you're done.

Not pretty.

This page will serve you well if your gas gauge is broken, inaccurate, or is otherwise giving you problems. Or if you just want to know how well your car is doing. Can also be used for possibly figuring out ways to improve your mileage.

Needless to say, one needs to know the miles driven, how much gas was used, and the price of the gas before the templates will be of any use to you. If you do not already have these numbers, Section I below has everything you need to know on how to get started.

" Ω " Handy Google calculator. Opens in a separate tab or window.
  • Both " / " and " ÷ " means divide.
  • After arriving at the calculator and before entering numbers, you will need to click its numbers box first to get its attention.

Distance Traveled Precalculation

_______________  -   _______________  =  _______________ 
New Odometer            Previous Odometer     Miles Driven
Reading                       Reading             
(When you refill          (From previous fill-up
the tank)                      of tank)

As previously mentioned, if you are just looking for approximate answers, then you can simply use the templates and call it a day. If you are looking for the most accurate results possible, see Section I.

How to Calculate Miles per Gallon Formula Template

______________  /  ______________  =  ______________ 
Miles Driven             Gallons Used            Miles per Gallon


  1. You drove 100 miles and used 5 gallons of gas.
  2. Your intuitive answer would be 20 miles-per-gallon. Your intuitive answer would be correct.
  3. 100 miles traveled, divided by 5 gallons of gas used, gives you 20 miles per gallon.
  4. 100/5 = 20 mpg.

How to Calculate Gas Cost per Mile Formula Template

______________  /  ______________  =  ______________ 
Price per Gallon       Miles per Gallon        Cost per Mile


  1. You paid $5 for a gallon of gas, and you get 10 miles-per-gallon (mpg).
  2. Your intuitive answer would be $.50 a mile. Your intuitive answer would be correct.
  3. $5 paid, divided by 10 miles traveled per gallon (mpg), gives you $.50 cost per mile.
  4. 5/10 = $.50 cost-per-mile

About Your Miles per Gallon Results...

So what does the miles-per-gallon answer actually tell you? It tells you that...

  • This particular vehicle,
  • being mechanically maintained at a given level of efficiency,
  • using a specific brand and grade of gasoline,
  • being filled at a particular time of day,
  • from a particular gas station and a particular pump at a particular  fill speed,
  • and being driven a certain commute route,
  • by a specific driver...
...gets so many miles per gallon.

If the numbers used to make the calculation were accurate, this can lead to some interesting experimentation. What if...

  • A different gas station or pump was used? Not all stations and pumps are the same.
  • A different pump fill speed was used? 
  • The tank was filled at a different time of day? Temperature affects fluid density, first thing in the morning is best; that is when the gas is coldest and most dense.
  • A different brand and/or grade of gasoline was used? See Section II.
  • A different commute route was tried?
  • Deficiencies were found as to the vehicle's maintenance?
  • The vehicle's ignition timing was experimented with (but staying within smog emission specifications)? See Section II.
  • The driver notices and alters a particular driving habit?
Probably other ideas might also come to mind over time. 

Section I - Using a Reasonably Scientific Method and Mistakes to Avoid

If you are looking to get the most accurate results possible, this procedure will help you do that. If you are just looking for an approximation, then you can skip it all and fill in the templates with your existing numbers.
  1. Pick a week, or other time period, when you will be doing your most typical driving pattern.
  2. Have two pens and paper in the car.
  3. Use the gas station you normally use. Fill the gas tank at your usual time. Note the pump number you are using. Note the pump speed you normally use. Do not top off. While waiting, write down your odometer reading, include tenths. If you have a trip-odometer, reset it to zero. Remember to not be distracted by all this to the point you forget to put back the gas cap.
  4. Commence with your week; the usual work commute, errands, etc. Combining your work commute with errands will increase your gas mileage, but only do so if it is what you intend to usually do. Continue your routine until you have less than a quarter-tank. Don't strive for a gas-gauge reading of empty unless it is what you normally do.
  5. Make sure you still have the pens and paper in your car.
  6. At the same time of day as before, return to your previous gas station.
  7. Attempt to use the same pump number you used before. Set to the same pump speed as before. While waiting: write down your odometer reading; write down your trip-odometer reading; include tenths from both. When the pump-handle clicks: write down how many gallons; and very definitely include tenths. Write down the price you paid per gallon. Save the receipt; if the gas station is at least half-coordinated, some or all of this information will be printed there for you. Does it match what's showing on the pump? Do not top off. If so inclined, reset trip-odometer to zero. And the gas cap thing again...
  8. Proceed with your normal routine. You'll do the calculations with the templates at your leisure.

Section II - List of Notes About Fuel Economy, Improving Gas Mileage and Saving Money

Tune-ups and tire pressure: These are the Big Two as to getting the best mileage. A couple notes...  Over-inflating tires increases gas mileage, but causes an immediate and significant increase in tire wear; so don't do that. Under-inflated tires reduce your mileage; and it doesn't do your sidewalls any good either. As for tune ups, spark plugs are especially important. A fouled or carbon-built-up plug reduces mileage drastically, not to mention it will probably cause you to flunk a smog check. A personal note: Two different mechanics quoted me a price of over $100 to change a set of 6 spark plugs, plus the inflated cost of the plugs. In both cases, I departed the premises immediately. I ended up changing the plugs myself, it's not that hard to learn to do. Buy yourself a Chilton or Haynes manual for your particular make and model of car, they have all sorts of useful information. Some auto parts stores even have tool-loaner programs if you don't want to buy your own.

Looking ahead and coasting up to stop lights: Is a close third.

Speed: Once you are above 40 mph or so; the faster you go, the lower your mileage.

Weight: If you are carrying excess, unnecessary weight in the trunk, it will:
  • Reduce mileage
  • Increase engine wear and tear
  • Wear out your brakes faster
Ethanol: Do you have ethanol-times-of-year versus non-ethanol-times-of-year? It can be interesting to make mileage comparisons between the two. You probably won't be happy with the ethanol results.

Gasoline Grade: Putting premium in a car that takes regular will do absolutely nothing for your mileage. However, if your car is in the midgrade octane category and what with there being some octane rating overlap, it might be worth experimenting with trying both the lower and higher octanes; especially if you are also experimenting with the ignition timing.

Temperature and humidity: Mileage is better during cooler times of the year than during heatwaves. And the higher the humidity, the better the mileage. Yep, one does get better mileage on rainy days.

Air filter: When is the last time you replaced the air filter? A clogged air filter does reduce mileage.

Fuel density and time of day: As mentioned earlier, always fill your tank first thing in the morning. Fluid density is affected by temperature. The colder it is, the more gas you get per gallon.

Logbook: If so inclined, this is as good a time as any to start one, especially if you want to try any of the aforementioned experiments..

A Couple of Relevant Federal Websites

I thought I'd include a couple of useful federal websites for your future reference. Both are worth browsing the next time you have some time to kill.

If only urban freeway traffic looked like this...
From Has all sorts of links regarding vehicles and fuel efficiency and saving gas in general.

For when planning your next road trip...
From This goes directly to their trip calculator page. What makes this calculator unique is you can specify the make and model of car you are using or are curious about. In addition to the total fuel cost calculation, they throw in a map and text directions as well. The rest of the site is also worth browsing.

Ohm's Law for How Many Watts, Volts, Amps, Etc.

Calculate Power and Watts; EMF and Volts; Current and Amps; Resistance and Ohms.

A handy math guide for those electrical or electronic math questions.

  • How to Quickly and Easily Find Electronics Answers
  • Using Ohm's Law and Its Derivatives
  • Electronics and Electrical Math Solutions
  • Includes Complete Lessons and Examples

(The templates alone might immediately provide the solution.)

It is guessed you are here to figure out a math answer to a particular electrical or electronics problem.

This is the place to figure out watts, amps, volts, or ohms from any of the other two by using Ohm's law and its derivatives. The math is surprisingly simple. You should have your answer in no time. Don't forget the templates and table of contents.

In most circumstances, the only math required is multiplication and division. Ohm's law and its derivatives uses some basic letters to represent watts, amps, volts, and ohms.
  • "P" is the industry standard to designate power by the unit of measurement, watts. "W" is sometimes used.
  • "I" is the industry standard to designate current by the unit of measurement, amps.
  • "E" and "V" are both used to designate electromotive-force by the unit of measurement, volts. The industry formula standard used to be "E", but now both "E" and "V" are being used interchangeably.
  • "R" is the industry standard to designate resistance by the unit of measurement, ohms.
And that's all there is to it. No degree in rocket surgery required. No need to memorize, definitions reprinted as needed.

If your inquiry concerns a particular appliance, device, etc.; check to see if there is any sort of specifications label, metal plate, or even just a sticker. Even if it doesn't provide the outright answer, it will hopefully have enough other information to enable you to calculate the answer from the templates.  If you happen to have the manual (maybe it is still online?), then you may become lucky indeed. As an example, if it tells you it consumes 200 watts and you know your house voltage is 120 volts, then you can easily calculate how many amps it uses and/or what its internal resistance in ohms will be.

" Ω " This handy, multi-purpose symbol (scattered here, there, everywhere for mobile users) opens the Google calculator in a separate tab or window.
  • Both " * " and " x " means multiply.
  • Both " / " and " ÷ " means divide.
  • "( )" means do whatever is inside the parenthesis first.
  • After arriving and before entering numbers, you will need to click its rectangular number-entry box first to get its attention.

Comprehensive List of Ohm's Law Formulas and Examples

Templates and Table of Contents

Here is a list of formulas and templates. With any luck, you will find one you can use and won't have to bother clicking the related title for the included lessons and examples.

Calculate how many WATTS from volts, amps, ohms.

P = EI          ______________  *  _______________  =  ______________
                         Volts                           Amps                           Watts

P = E2/R      ______________  /  _______________  =  ______________
                   Volts Squared                   Ohms                           Watts

P = I2R        ______________  *  _______________  =  ______________
                   Amps Squared                  Ohms                           Watts

Calculate how many AMPS from watts, volts, ohms.

I = P/E        ______________  _______________  =  ______________
                        Watts                         Volts                            Amps

I = E/R        ______________  /  _______________  =  _______________
                        Volts                         Ohms                            Amps

I = √(P/R)   Sq Rt  (  ____________  /  ____________  )   =   __________
                                  Watts                    Ohms                         Amps

Calculate how many VOLTS from amps, watts, ohms.

E = P/I        _______________  /  _______________  =  ______________
                       Watts                         Amps                            Volts

E = IR        _______________  *  _______________  =  ______________
                       Amps                         Ohms                            Volts

E = √(PR)   Sq Rt  (  ____________  *  ___________  )   =   __________
                                 Watt                       Ohms                       Volts

Calculate how many OHMS from volts, amps, watts.

R = E/I      _______________  /  _______________  =  _____________
                          Volts                           Amps                         Ohms

R = E2/P    _______________  /  _______________  =  _____________
                    Volts Squared                   Watts                         Ohms

R = P/I2     _______________  /  _______________  =  _____________
                        Watts                    Amps Squared                 Ohms


There are four, independent, separate tutorials on this page. Simply select the one in the table of contents specifically addressing that which you you wish to find. Each how-to segment includes examples. Thanks to the laws of physics; whether it be trying to calculate how many amps, watts, ohms, or volts; Ohm's law will always provide three different, possible ways for finding the answer.

Hopefully, between the specifications plate, manual(s), and the above math; you will be able to find the answer to your question. Otherwise...

What Is a VOM ( Electronics Definition ) And Some General Notes...

VOM is the acronym for Volt Ohm Milliammeter, More specifically, it is known as a multimeter or a multitester. The usual VOM can measure AC and DC voltage, current in milliamps, and resistance in ohms and megohms. For the purposes of this page, it is usually needed to find the resistance. Once the number of ohms are known, more of the templates and formulas can be used when the usual volt/amp/watt amounts aren't available.

When it comes to test instruments, skip the cheap ones. What a test instrument tells you will in turn cause you to make important decisions. As such, a quality test instrument is much more important than the usual RadioShack novelty toy, piece of wiring, batteries, etc. And whatever you do, do not buy a kit to make your own test instrument. Buying and building kits for other things is fine, but leave the VOM manufacturing to the professionals with the quality reputations (this is the voice of personal experience talking).

Do not buy a VOM until you truly know what you are doing. Cheaper meters are extremely inaccurate when it comes to measuring certain ranges of resistance, etc. Even voltage and milliampere measurements can be suspect. Really research the subject first.

Ohm's Law math lessons and examples follow or select from the Table of Contents.


How Many WATTS - How to Calculate or Convert Watts to and from Any Two of Either Volts, Amps, or Ohms.

(P=watts, E=volts, I=amps, R=ohms)

Includes amps to watts and volts to watts.

Watts is the composite measurement of electromotive force and current, otherwise known as voltage and amperage. It is how we quantify electrical energy amounts and usage.

Three ways to figure out the electrical energy amount, measured in watts...

#1. P = EI — Watts Are Equal to Volts Times Amps

 Ω (P=watts, E=volts, I=amps, R=ohms)

Ω  Some examples...

  • Tungsten filament light bulb. 120 volts times .8333 amps equals 100 watts. 120 * .8333 = 100
  • Microwave oven. 120 volts times 5.8333 amps equals 700 watts. 120 * 5.8333 = 700
  • Microwave oven. 120 volts times 9.1666 amps equals 1100 watts. 120 * 9.1666 = 1100
  • Some air conditioners. 240 volts times 4 amps equals 960 watts. 240 * 4 = 960
  • Car battery. 12 volts times 3 amps equals 36 watts. 12 * 3 = 36
  • Car voltage when engine is running. 14.5 volts times 3 amps equals 43.5 watts. 14.5 * 3 = 43.5
  • Car battery. 12 volts times 15 amps equals 180 watts. 12 * 15 = 180
  • Car voltage when engine is running. 14.5 volts times 15 amps equals 217.5 watts. 14.5 * 15 = 217.5
  • Most laptop batteries. 19 volts times 3.5 amps equals 66.5 watts. 19 * 3.5 = 66.5
Side note: the prefix, "milli", means one one-thousandth.
  • There are 1000 milliwatts in a watt.
  • There are a 1000 millivolts in a volt.
  • There are a 1000 milliamps in an amp.

 Ω More examples...

  • A toy using a 9-volt battery consumes 250 milliamps (.25 amps). Multiplying 9 volts by 250 milliamps calculates out to 2.25 watts. 9 * .25  = 2.25
  • A 350-millivolt subcircuit uses 455 milliamps (.455 amps). Multiplying 350 millivolts by 455 milliamps indicates that part of the circuit is using 159 milliwatts (rounded) of energy. 350 * 455 = 159.25
  • A 4.5 volt LED array uses 75 milliamps. Multiplying 4.5 volts by .075 shows the LED array consumes  337.5 milliwatts. 4.5 * .075 = 337.5

#2. P = E²/R — Watts Are Equal to Volts Squared Divided by Ohms

 Ω (P=watts, E=volts, I=amps, R=ohms)

 Ω Some examples...

  • 110 volts squared, then divided by 65 ohms equals 186.15 watts. 110²/65 = 12100/65 = 186.15
  • 120 volts squared, then divided by 125 ohms equals  115.2 watts. 120²/125 = 14400/125 = 115.2
  • 70 volts squared, then divided by 42 ohms equals 116.67 watts.70²/42 = 4900/42 =116.67
  • 12 volts squared, then divided by 24 ohms equals 6 watts. 12²/24 = 144/24 = 6
  • 12 volts squared, then divided by 100 ohms equals 1.44 watts. 12²/100 = 144/100 = 1.44
  • 6 volts squared, then divided by 100 ohms equals 360 milliwatts. 6²/100 = 36/100 = .36
  • A motor  requires 40 volts and has an internal resistance of 25 ohms. 40 volts squared, then divided by 25 ohms has a total energy usage of 64 watts. 40²/25 = 1600/25 = 64
  • There are 7.5 volts running through a component with 5 ohms resistance. Its wattage would be a total of 11.25 watts. 7.5²/5 = 56.25/5 = 11.25

#3. P = I²R — Watts Are Equal to Amps Squared Times Ohms

 Ω (P=watts, E=volts, I=amps, R=ohms) stopping point

 Ω Some examples...

  • 1 amps squared, multiplied by 30 ohms equals 30 watts. 1² * 30 = 1 * 30 = 30
  • 5 amps squared, multiplied by 30 ohms equals  750 watts. 5² * 30 = 25 * 30 = 750
  • 14 amps squared, multiplied by 2 ohms equals 392 watts.14² * 2 = 196 * 2 =392
  • 100 milliamps squared, multiplied by 30 ohms equals 30 milliwatts. .100² * 30 = .01 * 30 = .03
  • 334 milliamps squared, multiplied by 15 ohms equals 1.6725 watts. .334² * 15 = .1115 * 15 = 1.6725
  • 750 milliamps squared, multiplied by 5 ohms equals 2.8125 watts. .750² * 5 = .5625 * 5 = 2.8125


How Many AMPS - How to Calculate or Convert Amps to and from Any Two of Either Watts, Volts, or Ohms.

(I=amps, E=volts, P=watts, R=ohms)

Includes volts to amps and watts to amps..

It's current and amperage that makes those power meters spin and flips those fuse box switches and circuit breakers on occasion. The 1500-watt space heater is a good example. Microwave ovens can be a close second. An unexpected short circuit in an appliance or house wiring is what causes buildings to burn down if the circuit breaker doesn't do its job.

Three ways to figure out current in amps...

#1. I = P/E — Amps Are Equal to Watts Divided by Volts

 Ω (I=amps, E=volts, P=watts, R=ohms)

Ω  Some examples...

  • The aforementioned space heater. 1500 watts divided by 120 volts equals 12.5 amps current. 1500/120 = 12.5
  • The aforementioned microwave oven. 1100 watts divided by 120 volts equals 9.17 amps current. 1100/120 = 9.17
Turning both of those on at once will flip a 15-amp circuit breaker right there. A 20-amp circuit breaker wouldn't be too thrilled with it either.

Ω More examples...

  • 2 watts divided by 6 volts equals .33333 amps current. 2/6 = .34
  • 5 watts divided by 12 volts equals .416666 amps current. 5/12 = .417
Side note: the prefix, "milli", means one one-thousandth.
  • There are a 1000 millivolts in a volt.
  • There are a 1000 milliamps in an amp.
  • There are 1000 milliwatts in a watt.

 Ω More examples...

  • A 140-watt computer circuit board uses 360 volts from a step up transformer. This is not a circuit board you want to mess with. Dividing 140 watts by 360 volts shows a current of  389 milliamps running through it. 140/360  = .389 amps (or 389 milliamps)
  • A 300-milliwatt circuit board is connected to a 3-volt power supply. Dividing 300 milliwatts by 3 volts  indicates the circuit board requires a current of 100 milliamps (.1 amps). .3/3 = .1
  • A 20-watt device uses standard 120-volt house current. Dividing 20 watts by 120 volts reveals the device is using .1666 amps or 167 milliamps. 20/120 = .167

#2. I = E/R — Amps Are Equal to Volts Divided by Ohms

 Ω (I=amps, E=volts, P=watts, R=ohms)

 Ω Some examples...

  • 240 volts divided by 500 ohms calculates to a current of 480 milliamps. 240/500 = .480
  • 110 volts  divided by 2000 ohms calculates to a current of 55 milliamps. 110/2000 = .055
  • 12 volts  divided by 250 ohms calculates to a current of 48 milliamps. 12/250 = .048
  • A tiny, hobby motor needs 3 volts to operate and has an internal resistance of 40 ohms. 3 volts divided by 40 ohms indicates a usage of 75 milliamps. 3/40 = .075
  • There are 9 volts running through a controller with an internal resistance of 135 ohms. 9 divided by 135 equals a current usage of 67 milliamps. 9/135 = .066666

#3. I = √(P/R) — Amps Are Equal to the Square Root of the Quotient of  Watts Divided by Ohms

 Ω (I=amps, E=volts, P=watts, R=ohms)

Contrary to the general introduction, this third and last resort does involve the use of square roots; so break out the calculator, spreadsheet, or search engine if you haven't done so already.

Basically, all one does is divide watts by ohms; then just find the square root of the quotient to determine the amperage.

"" is the symbol for square root.

 ΩSome examples...

  • 100 watts divided by 4 ohms gives us a quotient of 25. The square root of 25 is 5 amps.  √(100/4) = √25 = 5
  • 900 watts divided by 5 ohms gives us a quotient of 180. The square root of 180 is 13.42  amps (rounded).  √(900/5) = √180 =13.4164
  • 40 watts divided by 40 ohms gives us a quotient of 1. The square root of 1 is 1 amp.  √(40/40) = √1 =1
  • 5 watts divided by 100 ohms gives us a quotient of .05. The square root of .05 results in an answer of 224 milliamps (rounded).  √(5/100) = √(.05) =.2236  Square roots of numbers less than 1.0 are odd that way.


How Many VOLTS - How to Calculate or Convert Volts to and from Any Two of Either Watts, Amps, or Ohms.

(E=volts, P=watts, I=amps, R=ohms)

Includes amps to volts and watts to volts.

Unlike with most watts and amps questions, voltage and voltage-drop questions usually have to do with circuit boards and their sub components. However, here are also some basics...
  • Typical US house voltage is 120 volts; though for certain appliances, voltage is boosted to 240 volts.
  • The car battery standard is 12 volts.
  • The laptop standard is most often 19 volts.
  • Standard carbon or alkaline batteries (whether sizes D, C, aa, aaa, etc.) are all 1.5 volts each. Putting them in series is simply additive. As an example, if you see a 6-volt flashlight being advertised, you know it will require four batteries.

Three ways to figure out volts...

#1. E = P/I — Volts Are Equal to Watts Divided by Amps

 Ω (E=volts, P=watts, I=amps, R=ohms)

Ω  Some examples...

  • 500 watts divided by 5 amps equals 100 volts. 500/5 = 100
  • 12 watts divided by .1 amps equals 120 volts. 12/.1 = 120
  • 150 watts divided by 2 amps equals 75 volts. 150/2 = 75
  • A 6-watt car instrument cluster has half an amp running through it. Is the car engine running or not? Dividing the 6 watts by .5 amps gives us 12 volts. The engine is off (when the engine is running the system voltage ranges from 14 to 14.5 volts). 6/.5 = 12
  • A 600-watt starter for a small engine requires 50 amps. Dividing 600 watts by 50 amps indicates that a 12-volt battery can indeed do the job. 600/50 = 12
Side note: the prefix, "milli", means one one-thousandth.
  • There are a 1000 millivolts in a volt.
  • There are a 1000 milliamps in an amp.
  • There are 1000 milliwatts in a watt.

 Ω More examples...

  • A 400-milliwatt (.4 watts) circuit board uses 80 milliamps (.080 amps). Dividing 400 milliwatts by 80  milliamps indicates it is connected to a 5-volt input. 400/80 = 5
  • A 180-milliwatt component uses 45 milliamps. Dividing 180 milliwatts by 45 milliamps equals 4 volts. 180/45 = 4

#2. E = IR — Volts Are Equal to Amps Multiplied by Ohms

 Ω (E=volts, P=watts, I=amps, R=ohms)

 Ω Some examples...

  • 10 amps multiplied by 12 ohms equals 120 volts. 10 * 12 = 120
  • 35 amps multiplied by 42 ohms equals 1470 volts. 35 * 42 = 1470
  • .5 amps multiplied by 6 ohms equals 3 volts. .500 * 6 = 3
  • An air conditioner  requires 50 amps. The motor, pump, and other circuitry has a total resistance of 4.8 ohms (surprisingly low actually). That A/C will require 240 volts to operate. 50 * 4.8 = 240
  • There are 600 milliamps running through a circuit with a measured resistance of 5 ohms. So that would be 600 milliamps times 5 ohms, giving you 3 volts. .600 * 5 = 3

#3. E = √(PR) — Volts Are Equal to the Square Root of the Product of Watts Times Ohms

 Ω (E=volts, P=watts, I=amps, R=ohms)

Contrary to the general introduction, this third and last resort does involve the use of square roots; so break out the calculator, spreadsheet, or search engine if you haven't done so already.

Basically, all one does is multiply watts times ohms; then just find the square root of the product to determine the voltage.

"" is the symbol for square root.

 Ω Some examples...

  • 14 watts multiplied by 10.285 (rounded) ohms equals a product of 144. The square root of 144 is 12 volts. √(144 * 10.285) = √144 = 12
  • 300 watts multiplied by 20 ohms equals a product of 6000. The square root of 6000 is 77.46 volts (rounded).  √(300 * 20) = √6000 = 77.46
  • A 900-watt microwave oven magnetron has an internal resistance of 15 ohms. 900 watts times 15 ohms gives a product of 13,500. The square root of 13,500 is 116 volts (rounded).  √(900 * 15) = √13500 = 116.2. What with house voltages ranging from 110 to 120 volts, that will work just fine.
Side note: the prefix, "kilo", means one thousand.
  • There are a 1000 volts in a kilovolt (kv).
  • There are a 1000 amps in a kiloamp (KA).
  • There are 1000 watts in a kilowatt. (kw).

 Ω An example...

  • 1,000 watts (1kw) multiplied by 10 ohms equals a product of 10,000. The square root of 10,000 is 100 volts.  √(1000 * 10) = √10000 = 100


How Many OHMS - How to Calculate or Convert Ohms to and from Any Two of Either Watts, Volts, or Amps.

(R=ohms, E=volts, I=amps, P=watts)

Unlike with most watts and amps questions, resistance and ohms questions usually have to do with circuit boards and their sub components. However, the internal resistance of an appliance or device greatly affects how much power it uses. The classic example of this is the incandescent, tungsten filament light bulb. A single, 100-watt bulb requires almost a full amp of current at 120 volts. That can add up fairly quickly over time. Power meters love it, everyone else hates it.

Three ways to figure out resistance in ohms...

#1. R = E/I — Ohms Are Equal to Volts Divided by Amps

 Ω (R=ohms, E=volts, I=amps, P=watts)

Ω  Some examples...

  • The aforementioned light bulb. 120 volts divided by .8333 amps equals 144 ohms resistance. 120/.8333 = 144
  • 240 volts divided by 3 amps equals 80 ohms resistance. 240/3 = 80
  • 12 volts divided by 1.50 amps equals 8 ohms resistance. 12/1.5 = 8
  • 19 volts divided by 2.3 amps equals 8.26 ohms resistance. 19/2.3 = 8.26
Side note: the prefix, "milli", means one one-thousandth.
  • There are a 1000 millivolts in a volt.
  • There are a 1000 milliamps in an amp.
  • There are 1000 milliwatts in a watt.

 Ω More examples...

  • A 9-volt circuit board uses 140 milliamps (.140 amps). Dividing 9 volts by 140 milliamps indicates the board has an internal resistance of 64.29 ohms (rounded). 9/.14 = 64.29
  • A 500-millivolt component uses 120 milliamps. Dividing 500 millivolts by 120 milliamps indicates the component has a resistance of 4.17 (rounded) ohms. 500/120 = 4.17
  • A 4.5 volt LED array uses 15 milliamps. Dividing 4.5 by .015 equates to a resistance of 300 ohms. 4.5/.015 = 300

#2. R = E²/P — Ohms Are Equal to Volts Squared Divided by Watts

 Ω (R=ohms, E=volts, I=amps, P=watts)

 Ω Some examples...

  • 120 volts squared, then divided by 100 watts equals a resistance of 144 ohms. 120²/100 = 14400/100 = 144
  • 50 volts squared, then divided by 35 watts equals a resistance of 71.43 ohms.50²/35 = 2500/35 = 71.43
  • 6 volts squared, then divided by 4 watts indicates a resistance of  9 ohms. 6²/4 = 36/4 = 9
  • A motor  requires 36 volts and uses 40 watts of power. 36 volts squared, then divided by 40 watts has a total resistance of 32.4 ohms. 36²/40 = 1296/40 = 32.4 
  • There are 1.5 volts running through a component using 2 watts. Its resistance would be 1.125 ohms.1.5²/2 = 2.25/2 = 1.125

#3. R = P/I² — Ohms Are Equal to Watts Divided by the Square of Amps

 Ω (R=ohms, E=volts, I=amps, P=watts)

Ω Some examples...

  • 150 watts divided by 7 amps squared. The 7 amps squared is 49, so we have 150 watts divided by 49; giving us an answer of 3.06 ohms. 150/7² = 150/49 = 3.06
  • 40 watts divided by by 20 amps squared. The 20 amps squared is 400, so we have 40 watts divided by 400, giving us an answer of .1 ohms or 100 milliohms. 40/20² = 40/400 = .1 We are pretty much looking at a 2-volt short circuit on a board that needs fixing, probably a shorted out capacitor.
  • A 500-watt refrigerator divided by 11 amps squared. 11 amps squared is 121, so we have 500 watts divided by 121, giving us an answer of 4.13 ohms (rounded).
  • A 5-watt circuit sub-board consumes 300 milliamps. So the equation is 5/.3² to give us the resistance in ohms. .3² is .09,  so we have 5/.09 = 55.56 ohms (rounded) in calculated resistance.

A Final Thought...

Do be careful. The laws of physics are unforgiving.