Fuel Economy Calculator

Convert fuel economy between mpg, L/100 km, and km/L, work it out from a trip, or estimate the fuel cost of a trip. The fuel economy calculator handles US and UK gallons.

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Fuel economy
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How to use the Fuel Economy Calculator

  1. Choose Convert units, From a trip, or Trip cost.
  2. Enter the fuel economy, or the distance and fuel used, or the trip distance, your economy, and the fuel price.
  3. Press Calculate. You get the converted figures, your fuel economy, or the trip cost.

How it works

L/100 km = 235.215 ÷ mpg (US)
L/100 km = 282.481 ÷ mpg (UK)
km/L = 100 ÷ (L/100 km)
from a trip: L/100 km = litres ÷ km × 100
trip cost = km × (L/100 km) ÷ 100 × price per litre

1 US gallon = 3.785 L, 1 UK gallon = 4.546 L, 1 mile = 1.609 km.

Examples

  • 30 mpg (US) = 7.84 L/100 km.
  • 500 km on 40 L = 8 L/100 km, or 12.5 km/L, 29.4 mpg (US), and 35.3 mpg (UK).

Why mpg and L/100 km run in opposite directions

Miles per gallon measures distance per unit of fuel, so higher is better. Litres per 100 km measures fuel per distance, so lower is better. Improving from 10 to 20 mpg saves far more fuel than from 30 to 40 mpg, which L/100 km makes easier to see.

Limitations

  • Real consumption depends on speed, load, weather, and driving style.
  • Electric vehicle efficiency (kWh/100 km) is not covered.

Frequently asked questions

How do I convert mpg to L/100 km?

Divide 235.215 by the US mpg figure, or 282.481 by the UK mpg figure.

Why is UK mpg higher than US mpg for the same car?

A UK gallon is about 20% larger than a US gallon.

How do I calculate my car's fuel economy?

Fill the tank, drive, refill, and divide the fuel used by the distance. Use the From a trip tab.

Often used together with the Fuel Economy Calculator.