Fuel Economy Calculator

Four Units, One Underlying Number

MPG (US), MPG (UK), L/100km, and km/L all describe the same underlying relationship — distance covered per unit of fuel — but they're not simple multiples of each other, and two of them run in the opposite direction (a lower L/100km is better, while a lower MPG is worse). Converting between them by hand invites rounding mistakes, especially since the US and UK gallon are different sizes.

The Formula

Every conversion in this calculator routes through L/100km as a common base, then converts out to the target unit — the same approach used internally by the calculator, which keeps every combination of units internally consistent.

Where This Matters

• Importing or comparing a foreign-market vehicle — a UK-spec economy figure isn't directly comparable to a US MPG rating without conversion, since the UK gallon is about 20% larger than the US gallon.
• Reading European fuel economy labels — most of continental Europe rates vehicles in L/100km, which needs conversion for anyone used to thinking in MPG.
• International road trip planning — converting a rental car's rated economy into a familiar unit makes fuel budgeting straightforward across borders.
• Spec sheet comparisons — automotive publications sometimes mix units across markets; converting to one common unit makes the comparison fair.

Fuel Economy Unit Conversion Reference

MPG (UK) = MPG (US) × 1.20095, reflecting the ratio between the US and imperial gallon.

How to Use This Calculator

1. Enter the value you want to convert.
2. Select the unit you're converting from: MPG (US), MPG (UK), L/100km, or km/L.
3. Select the unit you want to convert to.
4. Select Calculate to see the converted value.

Related Calculations

Calculate your own real-world figure first with the Mileage Calculator, then estimate trip costs with the Fuel Cost Calculator.