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Gas Mileage Calculator: MPG, L/100 km and km/L
Enter the distance you drove and the fuel you used, in any common units. The calculator reports fuel economy as US mpg, UK mpg, litres per 100 km and kilometres per litre, and can add the running cost per distance.
The fuel economy formulas
Fuel economy can be expressed two ways. Distance-per-fuel figures rise as efficiency improves, while fuel-per-distance figures fall.
MPG = miles ÷ gallons, used in the United States (US gallons) and the United Kingdom (imperial gallons).km/L = kilometres ÷ litres.L/100 km = litres ÷ kilometres × 100, common in Europe, Canada and many other countries.
Everything here is converted through exact definitions: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L and 1 imperial gallon = 4.54609 L. For the example above, 350 miles on 12.5 US gallons is 28 mpg, which equals about 8.40 L/100 km.
US gallons are not imperial gallons
An imperial gallon is about 20% larger than a US gallon, so the same car shows a higher number in imperial mpg. A vehicle that returns 28 mpg (US) returns about 33.6 mpg (UK). Comparing a US figure with a UK figure without converting is a frequent source of confusion when reading reviews or specifications from different countries. The page therefore shows both values side by side, and its headline follows the units you entered.
The inverse relationship matters too: L/100 km of 8.4 is better than 9.4, and a car going from 10 mpg to 20 mpg saves far more fuel than one going from 40 mpg to 50 mpg, even though both gain ten.
Measuring mileage accurately
The fill-up method gives the most dependable figure. Fill the tank completely, reset the trip meter, drive normally, then fill the tank completely again at the same pump if you can. Enter the trip distance and the volume that went in. One tank is a rough guide; averaging several tanks smooths out differences caused by traffic, weather, load and where the pump stopped.
The fuel computer in a vehicle can read a few per cent high or low, and odometers have small errors as well. Partial fills, topping up after the pump clicks off and driving different mixes of city and highway will all shift the number. Short trips with a cold engine tend to look worse than long steady ones.
Limits
This tool covers combustion engines measured by volume of fuel. It does not apply to electric vehicles, where energy is measured in kilowatt-hours. A warning appears when a result falls outside the range of plausible road-vehicle figures, which usually means the wrong unit was chosen. Use the result to track a vehicle over time; it is not a certified rating.
Worked example
A driver covers 350 miles between two full-tank fill-ups and then puts 12.5 US gallons back in, at 3.50 per gallon.
Inputs
| Distance driven | 350 |
|---|---|
| Distance unit | Miles |
| Fuel used | 12.5 |
| Fuel unit | US gallons |
| Fuel price per unit (optional) | 3.5 |
Result
Distance 563.3 km (350.0 miles) on 47.32 litres.
| Miles per US gallon | 28.00 |
|---|---|
| Miles per imperial gallon | 33.63 |
| Litres per 100 km | 8.40 |
| Kilometres per litre | 11.90 |
| Fuel cost for this trip | 43.75 |
| Cost per mile | 0.125 |
| Cost per kilometre | 0.078 |
- A lower L/100 km figure means better economy; a higher mpg or km/L figure means better economy.
Accuracy note: Results are calculated in your browser from the values you enter. Check anything that matters for legal, academic or financial purposes against the official source.
Frequently asked questions
How do I calculate miles per gallon?
Divide the miles driven by the gallons of fuel used. If you drove 350 miles and used 12.5 gallons, the result is 28 miles per gallon.
How do I convert MPG to L/100 km?
For US mpg, divide 235.215 by the mpg figure. For imperial mpg, divide 282.481 by it. A car with 28 mpg (US) uses about 8.4 litres per 100 kilometres.
Why does my UK mpg look higher than the US figure?
The imperial gallon holds about 4.546 litres and the US gallon about 3.785, so each imperial gallon takes you further. The ratio is roughly 1.2.
How many tanks should I average?
Three to five consecutive fill-ups usually give a stable figure. A single tank can be skewed by one long motorway trip or a spell in heavy traffic.
Does the calculator work for electric cars?
No. It is built for fuel measured in gallons or litres. Electric vehicles use kilowatt-hours per distance, which needs a different unit and a different formula.