Work out a vehicle’s real fuel economy from the distance driven and the fuel used, shown at once as MPG, L/100 km and km/L.
Add one row per fill-up. Each row is a distance covered and the fuel it took to top the tank back up. The calculator totals every row and works out the overall economy.
Optional: add a fuel price to see running cost
| Measure | Value | What it means |
|---|---|---|
| MPG (US) | - | Miles travelled per US gallon. Higher is better. |
| L/100 km | - | Litres burned every 100 km. Lower is better. |
| km/L | - | Kilometres travelled per litre. Higher is better. |
| Cost per 100 mi | - | Fuel money for every 100 miles driven. |
| Cost per 100 km | - | Fuel money for every 100 kilometres driven. |
Add a fuel price in the optional section above to also see the fuel cost per 100 mi and per 100 km.
The marker shows where this vehicle sits between a thirsty engine and an economical one, measured in MPG (US).
For beginners: how to read this result
Start by choosing your unit system: Imperial measures distance in miles and fuel in US gallons, while Metric uses kilometres and litres. The two core inputs are the distance you drove and the fuel it took to refill the tank after that distance.
The two measuring modes
The mode toggle changes which fields appear.
- Single fill-up shows one distance field and one fuel field. Use it when you have measured a single tank: fill up, reset the trip odometer, drive, then refill, and the fuel needed to refill is the fuel that distance used.
- Multiple fill-ups shows an editable list of rows, one per fill-up. The calculator adds up every row’s distance and fuel and works out one overall economy figure. Averaging several real fill-ups across town and highway driving gives a far more honest everyday number than a single lucky tank.
How the figures are worked out
Miles per US gallon is simply the miles driven divided by the US gallons used. Litres per 100 km is the litres used divided by the distance in hundreds of kilometres, so a lower number is better because it counts fuel rather than distance. Kilometres per litre is the distance in kilometres divided by the litres used. All three describe the same drive, just framed differently. Unit conversion uses one US gallon equals 3.78541 litres and one mile equals 1.60934 kilometres, so a result entered in one system reads correctly in the other.
Fuel cost and the comparison bar
If you enter a fuel price in the optional section, the calculator also shows the fuel cost for every 100 miles and every 100 kilometres, which is the fairest way to compare two cars or two routes because the distance is held fixed. The comparison bar places your result between three reference bands – thirsty, average and economical – so a raw number becomes an easy-to-read verdict.
What is not included
This is an arithmetic estimate from the numbers you enter. It does not estimate tank range, emissions or the cost of a specific named journey, and it uses the US gallon rather than the Imperial gallon. Real economy changes with speed, load, terrain, weather, tyre pressure and driving style, and pump prices vary by region and date, so always enter your own measurements and local price.