How to Calculate Gas Mileage (MPG) and Fuel Costs per Mile

How to figure your car's miles per gallon and fuel costs. Includes quick and easy formulas and using templates (enclosed in green brackets).

Not a pretty picture...
Not a pretty picture... | Source

Guide on Figuring your Gas Mileage

Getting the numbers needed for doing the math

If you are looking to get the most accurate results possible, this method accomplishes that. Or you can skip it all and just use the two, easy, miles-per-gallon and costs-per-gallon formula templates.They are enclosed within the two pairs of horizontal, green, bracketing lines further down the page.

This page will also serve you well if your gas gauge is broken, inaccurate, or is otherwise giving you problems.

  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 first thing in the morning. 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 that 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. First thing on the appropriate morning, 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 when it is convenient for you to do so.

Math Calculations for Miles per Gallon

How to calculate your miles-per-gallon and fuel costs per mile.
How to calculate your miles-per-gallon and fuel costs per mile. | Source
  1. Subtract the smaller odometer reading from the larger odometer reading. Does the answer match the trip-odometer reading? If not, use your smaller-from-larger-odometer-answer, not the trip odometer number; as an extra, you now know how reliable your trip-odometer is.
  2. Divide your number-of-gallons into your odometer answer. Or to put it another way...
  3. Divide your odometer answer by your total number of gallons.
  4. You now have your miles-per-gallon answer. This is your mileage.
  5. As a cross-check, multiply your miles-per-gallon answer by the number-of-gallons. Does it match your odometer answer? If so, then you did the calculations correctly.


You drove 100 miles and used 5 gallons of gas:

Your intuitive answer would be 20 miles-per-gallon. Your intuitive answer would be correct.

100 miles travelled, divided by 5 gallons used, gives you 20 miles per gallon.

100/5=20 mpg

You drove 410 miles and used 15.5 gallons of gas:

410 miles travelled, divided by 15.5 gallons of gas used, equals 26.45 miles-per-gallon (rounded).

410/15.5=26.45 mpg

You drove 253.5 miles and used 13.2 gallons of gas:

253.5 miles travelled, divided by 13.2 gallons of gas used, equals 19.20 miles-per-gallon (rounded).

253.5/13.2=19.20 mpg

Miles per Gallon Formula

Template – To calculate miles per gallon...

_______________ / _______ = ___________________
distance travelled... gas used... miles per gallon (mpg)

Metric – Kilometers-per-Liter

The procedure for metric is the same of course.

  • Divide your odometer answer by the number-of-liters on the pump.

The resulting answer being kilometers-per-liter.

Math Calculations for Cost of Gas per Mile

Gas Cost per Mile Formula
Gas Cost per Mile Formula | Source

Just divide your miles-per-gallon into your price per gallon; otherwise stated as, divide your price-per-gallon by your miles-per-gallon.


You paid $5 for a gallon of gas, and you get 10 miles-per-gallon (mpg)

Your intuitive answer would be $.50 a mile. Your intuitive answer would be correct.

$5 paid, divided by 10 miles travelled per gallon (mpg), gives you $.50 cost per mile.

5/10=$.50 cost-per-mile

You paid $5.30 per gallon of gas, and you get 26.45 miles-per-gallon (mpg):

$5.30 paid, divided by 26.45 mpg, gives you a cost of $.20 per mile

5.30/26.45=$.20 cost-per-mile

You paid $4.24 per gallon of gas, and you get 19.20 miles-per-gallon (mpg):

$4.24 paid, divided by 19.20 mpg, gives you a cost of $.22 per mile

4.24/19.2=$.22 cost-per-mile

Fuel Cost per Mile Formula

Template – To calculate fuel cost per mile...

______________ / ________ = _________________
price per gallon......... mpg.......... cost per mile

Improving Fuel Economy

Odds & Ends

Tune-ups and tire pressure: These are the Big Two as to getting the best mileage. A note: over-inflating tires causes a significant increase in tire wear; so don't do that...

Coasting up to stop lights and stop signs: 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 your 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.

Temperature and humidity: Mileage is better during cooler times of the year than during heatwaves. The higher the humidity, the better the mileage.

Air filter: When is the last time you replaced the air filter?

Logbook: If so inclined, this is as good a time as any to start one.

It is hoped this page gave you the information you were looking for. May all your miles be peaceful ones. And if you are looking for more maintenance tips, you can find them here.

And for your amusement...

The most ridiculous car chase ever.

I wonder what kind of mileage she got...

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