MPG Calculator
Work out your real fuel economy from a trip's distance and fuel used, or from two full-to-full fill-ups -- shown in mpg (US), mpg (UK), L/100 km and km/L at once.
mpg (US)
27.2
mpg (UK)
32.7
L/100km
8.6
km/L
11.6
How it's calculated
Both entry methods reduce to the same underlying formula -- distance traveled divided by fuel used -- converted to liters per 100 km internally, then reported in all four common units:
L/100km = (fuel used, in liters ÷ distance, in km) × 100
mpg (US) = 235.21 ÷ L/100km · mpg (UK) = 282.48 ÷ L/100km · km/L = 100 ÷ L/100km
Worked example
The calculator's own defaults: 340 miles driven on 12.5 gallons (US).
| mpg (US) | 27.2 |
| mpg (UK) | 32.7 |
| L/100 km | 8.6 |
| km/L | 11.6 |
Frequently Asked Questions
What's the difference between the trip and full-to-full methods?
Trip mode uses a distance and a fuel amount you already know. Full-to-full mode uses two odometer readings and the fuel added at the second fill-up -- since the tank was full both times, the fuel added at fill-up two is exactly what was used to cover the distance since fill-up one. Full-to-full is the more accurate real-world method, because it doesn't depend on a trip computer's own estimate.
Why does my mpg (UK) number look higher than mpg (US)?
The imperial (UK) gallon holds about 20% more than a US gallon, so the same car needs fewer of the larger unit to go the same distance, making the mpg (UK) figure larger for an identical vehicle. Neither number is 'more efficient' -- they're the same real fuel economy in two different units.
Does this work for diesel and hybrid vehicles too?
Yes -- the calculation is the same regardless of fuel type or drivetrain: distance traveled divided by fuel actually used. It measures your real-world result, not a fuel-type-specific formula.
How many fill-ups should I average before trusting the number?
One full-to-full fill-up gives a real, usable number, but averaging three or more smooths out variation from a partial fill, a change in driving conditions, or a pump that shut off early.
These are estimates; real consumption varies with driving, load and conditions. This site isn't affiliated with any vehicle manufacturer, utility, or the US Energy Information Administration -- see the Terms.