# What is my gas mileage?

Works out a car’s gas mileage from the distance driven and the fuel used, in miles per gallon (US and UK), liters per 100 km, km per liter, and gallons per 100 miles.

- Page: https://www.acalculator.org/everyday-life/gas-mileage-calculator
- JSON spec: https://www.acalculator.org/everyday-life/gas-mileage-calculator.json
- Version: c5ff0bfa8be8

## Default answer

Example with the default inputs (Distance driven 300 mi, Fuel used 10 gal): 300 mi on 10 gal is 30 mpg, or 7.84 L/100 km.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| dist | Distance driven | The distance driven since the tank was last filled: new odometer reading − old reading. |
| fuel | Fuel used | The fuel it took to fill the tank again. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| mpg | Miles per gallon | Miles driven ÷ US gallons used. |
| l100 | Liters per 100 km | Liters used for every 100 kilometers: liters ÷ kilometers × 100. |
| kml | Kilometers per liter | Kilometers driven ÷ liters used. |
| mpgUk | Miles per UK gallon | Miles driven ÷ imperial gallons (4.54609 L) used. |
| gal100 | Gallons per 100 miles | US gallons used for every 100 miles, as on the EPA fuel economy label. |

## Method

mpg = miles driven ÷ gallons used; L/100 km = liters used ÷ kilometers driven × 100

## Assumptions

- Fill the tank completely both times, so the fuel you add equals the fuel used since the last fill.
- A US gallon is 3.785411784 L, a UK gallon 4.54609 L, and a mile 1.609344 km, all exact.
- Results are exact from the typed numbers and show to 2 decimal places, rounded half up.

## Worked examples

1. dist = 573,248.3328, fuel = 0.051103 gives mpg = 26.385185, l100 = 8.914646, gal100 = 3.790006. Source: Fueleconomy.gov, Calculating Your MPG: 356.2 miles ÷ 13.5 gallons = 26.4 mpg (https://fueleconomy.gov/mpg/MPG.do?action=calcMPG).
2. dist = 482,803.2, fuel = 0.037854 gives mpg = 30, l100 = 7.840486, kml = 12.754311, mpgUk = 36.028498. Source: NIST SP 811 (2008), Appendix B: 1 gal = 3.785411784 L and 1 mi = 1.609344 km exactly.
3. dist = 500,000, fuel = 0.04 gives l100 = 8, kml = 12.5, mpg = 29.401823. Source: NIST SP 811 (2008), Appendix B.

## FAQ

### How do I calculate my gas mileage?

Fill the tank and note the odometer. At the next fill-up, note the odometer again and the gallons it took to fill the tank. Divide the miles driven by the gallons. fueleconomy.gov’s example: 356.2 miles ÷ 13.5 gallons = 26.4 mpg.

### How do I convert mpg to L/100 km?

Divide 235.215 by the mpg. 30 mpg is 235.215 ÷ 30 = 7.84 L/100 km. The same number converts back: 235.215 ÷ 7.84 = 30 mpg. It comes from 100 × 3.785411784 L per gallon ÷ 1.609344 km per mile.

### Why is L/100 km better when it is lower?

mpg measures distance per fuel, so higher is better; L/100 km measures fuel per distance, so lower is better. Fuel per distance also shows savings directly: going from 10 to 8 L/100 km saves 2 liters every 100 km.

### Why is UK mpg higher than US mpg?

A UK (imperial) gallon is 4.54609 liters and a US gallon 3.785411784 liters, so a car goes further on a UK gallon. 30 US mpg is 36.03 UK mpg.

### Why is my mpg lower than the EPA rating?

EPA ratings come from set laboratory test cycles. Short trips, high speed, cold weather, air conditioning, heavy loads and hard acceleration all use more fuel, so real mileage often differs from the label.

### What does gallons per 100 miles mean?

It is the fuel used to drive 100 miles, shown on the EPA fuel economy label. 30 mpg is 100 ÷ 30 = 3.33 gallons per 100 miles.

## Sources

- U.S. Department of Energy and U.S. EPA, fueleconomy.gov, Calculating Your MPG: miles driven ÷ gallons used, with the 356.2 miles on 13.5 gallons example. https://fueleconomy.gov/mpg/MPG.do?action=calcMPG
- NIST SP 811 (2008), Appendix B: 1 US gallon = 3.785411784 L and 1 mile = 1.609344 km exactly.
- Weights and Measures Act 1985 (UK), Schedule 1: 1 gallon = 4.54609 liters.