MPG vs L/100km: How to Compare Fuel Economy
Fuel economy is measured two different ways around the world, and they run in opposite directions. Mixing them up leads to wrong comparisons. Here is how the two systems relate and how to convert and budget correctly.
Two ways to measure the same thing
MPG (miles per gallon) and km/L measure distance per unit of fuel — higher is better. L/100km measures fuel used per fixed distance — lower is better. They describe the same efficiency from opposite ends.
Why it is not a simple multiplication
Because one is distance-per-fuel and the other is fuel-per-distance, converting means dividing, not scaling. For US gallons: L/100km = 235.21 ÷ mpg, and mpg = 235.21 ÷ L/100km.
Example: 8 L/100km ≈ 29.4 MPG (US). The Fuel Economy Converter handles US, UK and km/L correctly so you never mix them up.
From economy to actual cost
Efficiency only matters in money terms once you add distance and fuel price. The Fuel Cost Calculator turns distance, consumption and price into the cost of a trip — useful for road trips and commuting budgets.
A quick tip
- Comparing two cars? Convert both to the same unit first.
- Small L/100km changes at low consumption matter more than the same change at high consumption.
- US and UK gallons differ — a UK gallon is about 20% larger, so UK MPG figures look higher.
Related tools
Last updated: July 6, 2026