Gas Mileage Calculator
Calculate actual fuel economy from an odometer interval or a known distance and fuel amount. Results include US MPG, imperial MPG, km/L and L/100 km.
Fuel-economy result
Gas mileage formulas
The calculator converts every entry to miles and US gallons, then derives all four common fuel-economy formats.
- US MPG = miles traveled ÷ US gallons used.
- km/L = kilometers traveled ÷ liters used.
- L/100 km = liters used ÷ kilometers traveled × 100.
- Imperial MPG = miles traveled ÷ imperial gallons used.
- Fuel cost per mile = fuel used × price per unit ÷ miles traveled.
Conversions use exactly 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L and 1 imperial gallon = 4.54609 L.
Checked examples
| Distance and fuel | US MPG | L/100 km |
|---|---|---|
| 300 mi and 10 US gal | 30.00 | 7.840 |
| 500 km and 40 L | 29.402 | 8.000 |
| 362 mi and 11.4 US gal | 31.754 | 7.408 |
How to measure real gas mileage
- Fill the fuel tank to a repeatable level and record the odometer.
- Drive normally. A longer interval generally reduces the effect of pump shutoff variation.
- Refill to the same level and record both the new odometer and the fuel added.
- Enter the readings here. The difference between odometers is the distance traveled.
A single tank is only one observation. Weather, traffic, speed, idling, towing, elevation, tire pressure, fuel blend and pump shutoff can change the result. Track several full-tank intervals for a more representative average.
Frequently asked questions
Is higher MPG better?
Yes. MPG and km/L measure distance per unit of fuel, so higher is better. L/100 km measures fuel per distance, so lower is better.
Can I use a partial fill-up?
Only if the beginning and ending fuel levels are known accurately. The common full-tank method assumes the fuel added at the end replaces the fuel consumed during the measured interval.
Why does displayed MPG differ from this result?
Dashboard estimates can use different averaging periods and sensor data. This calculation uses only the distance and fuel you enter, and pump-fill variation can affect one-tank results.
Does the comparison include maintenance or ownership costs?
No. It compares fuel use and fuel cost at the entered price. Financing, maintenance, insurance and depreciation are outside this calculator.
Related calculators
Use the Fuel Cost Calculator to estimate fuel, tolls and shared expenses for a planned route. Compare gasoline and electric driving costs with the Electric Vehicle Savings Calculator. Changing tires? Use the Tire Size Calculator to compare diameter, speedometer error and corrected distance.
Submitting work travel? Apply an employer or agency rate, add eligible expenses and subtract advances with the Mileage Reimbursement Calculator.