MPG & Fuel Efficiency Calculator

Calculate miles per gallon from distance and fuel used, or instantly convert between MPG, L/100km, and km/L to compare fuel efficiency across vehicles.

Calculate MPG from a fill-up

I drove
miles
and used
gallons

Convert fuel efficiency units

Enter any one value — the others update instantly.

MPG vs L/100km vs km/L — Which Should You Use?

All three metrics describe the same thing — fuel economy — just in different directions:

  • MPG (miles per gallon) — used in the UK and USA. Higher is better.
  • L/100km (litres per 100 kilometres) — used across Europe, Australia, and Canada. Lower is better.
  • km/L (kilometres per litre) — used in Japan, India, and parts of Asia. Higher is better.

When comparing vehicles across markets, always verify which gallon definition (UK vs US) is being used — a 40 MPG UK car is only ~33.3 MPG on the US scale.

Frequently Asked Questions

Divide the number of miles driven by the gallons of fuel used. For example, if you drove 300 miles on 8.5 gallons, your MPG is 300 ÷ 8.5 = 35.3 MPG.

A UK (imperial) gallon is 4.546 litres, while a US gallon is 3.785 litres. This means UK MPG figures are about 20% higher than US MPG for the same vehicle. For example, 40 UK MPG ≈ 33.3 US MPG.

For UK MPG: L/100km = 282.48 ÷ MPG. For US MPG: L/100km = 235.21 ÷ MPG. This tool handles both conversions automatically.

km/L is fuel efficiency expressed as distance per unit of fuel (higher is better, like MPG). L/100km is how many litres to travel 100 km (lower is better). To convert: km/L = 100 ÷ L/100km.