Fuel Economy Calculator
Convert between L/100km, km/L and miles-per-gallon (US).
Inputs
- Distance travelled
- Distance unit
- Fuel used
- Fuel unit
What it does
Converts a distance and the fuel used into L/100 km, km/L and US miles per gallon.
Where it's used
Comparing cars, tracking your own consumption and trip planning.
How to use it
- Enter the distance and its unit.
- Enter the fuel used and its unit.
- Read all three economy figures.
The formula explained
- L/100 km
- litres used per 100 km — lower is better
- km/L
- kilometres per litre — higher is better
- mpg (US)
- miles per US gallon (3.785 L)
Worked example
300 miles on 10 US gallons.
Inputs:
- Distance travelled: 300
- Distance unit: Miles
- Fuel used: 10
- Fuel unit: US Gallons
The calculator gives:
- Result: 7.84 L/100km
- km / L: 12.75
- Miles per US gallon: 30
Tips and common mistakes
- A UK gallon (4.546 L) is bigger than a US gallon; this calculator uses US gallons.
- Measure over a full tank (fill-to-fill) for accurate numbers.
- Short trips and idling make consumption worse.
Questions people ask
How do I convert L/100 km to mpg?
US mpg = 235.21 / (L/100 km), and UK mpg = 282.48 / (L/100 km). So 7.84 L/100 km is 30 US mpg, or about 36 UK mpg.
Why do many countries use L/100 km instead of km/L or mpg?
L/100 km is proportional to the fuel you actually burn, so savings are easy to compare. In mpg the steps mislead: going from 10 to 20 mpg saves 5 gallons per 100 miles, but going from 30 to 50 mpg saves only about 1.3.
How far will a full tank take me?
Tank size ÷ consumption × 100. A 45 L tank at 7.84 L/100 km gives about 574 km — keep a reserve, since consumption varies with traffic and speed.
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Enter your values to get the result with the formula, substituted values and an explanation of each step.