MPG & Fuel Consumption Calculator
Fill the tank, drive, fill it again: enter the distance and the fuel it took and this MPG calculator shows your real fuel economy in every unit, plus your fuel cost per mile or km.
Since your last full tank
How to work out your real MPG
- Fill the tank until the pump clicks off, and reset the trip meter (or note the odometer).
- Drive normally until the tank is at least half empty. The longer you go, the more accurate the result.
- Fill up again to the click, at the same pump if you can, and note how much fuel went in.
- Enter the distance and the fuel in the calculator. The fuel you just added is the fuel you used.
L/100 km = litres used ÷ km driven × 100
In the UK, petrol is sold in litres but MPG uses imperial gallons. Enter the litres from your receipt with the distance in miles and the calculator gives UK MPG; there's no need to convert first.
Why your MPG is different from the official figure
Official figures (EPA in the US, WLTP in the UK and Europe) come from standard lab tests. Your own figure depends on speed, traffic, weather, tyre pressure, load and how often you use the air conditioning. Short trips in cold weather use far more fuel than steady motorway cruising, so a car's real MPG often varies by 20% or more through the year. Measure over a few tanks and use the average when you calculate the fuel cost of a trip.
Is the trip computer accurate?
The average shown on the dashboard is calculated from injector data and is often a few percent more optimistic than a brim-to-brim measurement. Checking it against the calculator above once in a while tells you how far off it is.