MPG Calculator
Calculate vehicle miles per US gallon and its reciprocal fuel consumption rate.
How the result changes
Only distance driven changes; all other inputs stay at your current values. The line illustrates the formula across the shown range. This is not a forecast of real-world outcomes.
About this calculation
Fuel economy compares distance actually driven with fuel actually used. This MPG calculator also displays US gallons per 100 miles, a reciprocal view that makes the quantity of fuel for a fixed distance easier to compare. Calculate MPG when planning a trip or vehicle expense.
Formula
miles per gallon = distance in miles ÷ US gallons used
Worked example
With Distance driven: 315 mi, Fuel consumed: 10.5 US gal, fuel economy is 30 mpg.
Inputs and units
Enter a trip distance in statute miles and the US gallons consumed over that same trip. A full-tank measurement needs comparable fill levels at the beginning and end; a dashboard estimate may use different averaging.
- Distance driven (mi): Use miles from the same trip or refill interval as the fuel amount.
- Fuel consumed (US gal): Enter US gallons consumed over that exact distance.
Calculation and worked example
Divide miles by gallons to get miles per US gallon. Divide gallons by miles and multiply by 100 to get fuel per 100 miles. The two results are mathematically linked but their numeric scales move in opposite directions In compact notation, miles per gallon = distance in miles ÷ US gallons used.
A trip of 315 miles using 10.5 US gallons produces 30 mpg. The reciprocal measure is 10.5/315 × 100, or about 3.333 US gallons per 100 miles.
How to use the answer
Higher MPG means more distance from each gallon; lower gallons per 100 miles means less fuel for a fixed 100-mile route. They describe the same observation, so a difference between them signals mismatched or mistyped inputs.
Compare repeated fill-up intervals in similar driving conditions, or estimate fuel for a route after establishing a representative MPG. Traffic, speed, load, weather, and tyre pressure can change the observed figure.
Assumptions and checks
Distance and fuel refer to the identical interval and use US gallons, not imperial gallons. This tool does not adjust for odometer calibration, idle fuel outside the interval, or partial refills.
Do not divide gallons by miles and label it MPG; that is a consumption rate with different units. Mixing kilometres with miles or imperial gallons with US gallons also changes the answer substantially.
Multiply the mpg result by gallons used; it should reconstruct the entered miles. At exactly 100 miles, the second output equals the number of gallons consumed.
Common questions
What does the fuel economy result represent?
It is the number of statute miles travelled for each US gallon consumed during the entered observation interval.
What should I check before relying on this result?
Verify that both readings cover the same trip and that the volume really uses US gallons. Repeat measurements for a more representative average.
Inputs
- Distance driven (mi)
- Fuel consumed (US gal)