What is miles per gallon (MPG)?
Miles per gallon (MPG) is how far a car goes on one gallon of gas. The higher the number, the less gas you buy for the same drive.
How to calculate MPG
Fill the tank completely and write down the odometer reading. At your next fill-up, fill it completely again and write down the gallons and the new reading. Miles driven ÷ gallons = MPG.
Here it is with your numbers:
- Divide the miles by the gallons: 356.2 ÷ 13.5 = 26.3852.
- Round to one decimal: 26.4 MPG.
It means the car goes 26.4 miles on each gallon of gas.
Source FuelEconomy.gov (U.S. Department of Energy and EPA) · How to Calculate Your MPG ↗
MPG to L/100 km and km/L
Outside the US, fuel use is usually given in liters per 100 kilometers (L/100 km) or kilometers per liter (km/L). A mile is exactly 1.609344 km and a US gallon is exactly 3.785411784 liters, so L/100 km = 235.2146 ÷ MPG, and km/L = MPG × 1.609344 ÷ 3.785411784. Some charts round 235.2146 to 235.215; we use the exact figure.
Source NIST Handbook 44 (2026) · Appendix C, General Tables of Units of Measurement ↗
| MPG | L/100 km | km/L |
|---|---|---|
| 10 | 23.5 | 4.3 |
| 15 | 15.7 | 6.4 |
| 20 | 11.8 | 8.5 |
| 25 | 9.4 | 10.6 |
| 30 | 7.8 | 12.8 |
| 35 | 6.7 | 14.9 |
| 40 | 5.9 | 17.0 |
| 45 | 5.2 | 19.1 |
| 50 | 4.7 | 21.3 |
| 60 | 3.9 | 25.5 |
Why gallons per 100 miles?
MPG can mislead when you compare cars. Over 1,000 miles, going from 10 to 15 MPG saves about 33 gallons, but going from 30 to 35 MPG saves only about 5. That's why FuelEconomy.gov says fuel use, such as gallons per 100 miles, can be more meaningful than MPG.
Source FuelEconomy.gov · Learn More About the Fuel Economy Label for Gasoline Vehicles ↗
FAQs
How do I calculate gas mileage?
Divide the miles you drove by the gallons it took to refill the tank. Fill up completely and note the odometer; at the next full fill-up, note the gallons and the new reading. 33,001.3 − 32,645.1 is 356.2 miles, and 356.2 ÷ 13.5 gallons is 26.4 MPG.
Source FuelEconomy.gov (U.S. Department of Energy and EPA) · How to Calculate Your MPG ↗
How do you manually calculate MPG?
Reset the trip odometer when you fill the tank. At the next fill-up, divide the trip miles by the gallons you put in. 335 miles on 9.5 gallons is 35.26, so 35.3 MPG. (FuelEconomy.gov's own page prints 35.5 for this example, but 335 ÷ 9.5 is 35.26.)
How do I find the MPG of my car?
Measure it: fill the tank completely both times and divide the miles by the gallons, or log several fill-ups for a steadier average. A tank that isn't filled all the way makes the answer wrong.
Sources
- FuelEconomy.gov (U.S. Department of Energy and EPA): How to Calculate Your MPG
- FuelEconomy.gov: Learn More About the Fuel Economy Label for Gasoline Vehicles
- NIST Handbook 44 (2026): Appendix C, General Tables of Units of Measurement