Fuel Economy Converter

What Is a Fuel Economy Converter?

A fuel economy converter translates how far a vehicle travels per unit of fuel — or how much fuel it uses per distance — between units: miles per gallon, litres per 100 km, kilometres per litre. The catch is that these aren't all the same kind of measure. MPG and km/L are 'distance per fuel' (higher is better), while L/100km is 'fuel per distance' (lower is better), so converting between them is an inverse relationship, not a simple factor.

This converter handles that reciprocal math for you, and keeps US and UK gallons distinct — a US gallon is 3.785 L and an imperial gallon 4.546 L, so '40 mpg' means different efficiencies in the two countries. Enter a figure in any unit and read the true equivalent across all systems.

This is one category of the full Unit Converter — pair it with our percentage calculator or scientific calculator for related everyday maths.

Core Fuel Economy Conversions

These are reciprocal, not linear — divide a constant by the value to flip between the two measure types.

How to Use the Fuel Economy Converter

1. 1

   Enter the economy value

   Type the fuel-economy figure you want to convert — a window-sticker mpg, a trip-computer L/100km, a km/L reading.

2. 2

   Choose the 'from' unit carefully

   Pick US mpg, UK mpg, L/100km, or km/L. Mind which gallon and which measure type.

3. 3

   Choose the 'to' unit

   Select the target unit, or swap the two to reverse direction.

4. 4

   Read every unit at once

   The all-units table shows the economy in US mpg, UK mpg, L/100km, and km/L together — with the reciprocal handled for you.

Best Practices for Fuel Economy Conversion

• ✓Remember it's reciprocal. MPG and L/100km are inverse measures. Use 235.215 ÷ mpg (US), not a linear factor — and never average mpg figures directly.
• ✓Specify US or UK gallon. An mpg figure is meaningless without the gallon. US and imperial differ ~20%, so the same number is a different real economy.
• ✓Lower L/100km is better; higher mpg is better. The two measures run in opposite directions. Don't compare them as if bigger always means more efficient.
• ✓Don't average economy over a trip naively. Because of the reciprocal, average fuel use is total fuel ÷ total distance — not the mean of segment mpg figures.
• ✓Match the unit to the audience. Use mpg for US/UK readers and L/100km for metric ones; converting keeps a spec meaningful wherever it's read.

Why Fuel Economy Conversion Matters

Fuel economy decides running costs and is compared across borders constantly — but it's the trickiest everyday conversion because mpg and L/100km are reciprocal measures running in opposite directions, and 'mpg' itself splits into US and UK versions ~20% apart. Mishandle the reciprocal and a thrifty car looks like a gas-guzzler, or two cars get ranked backwards.

With fuel costs and emissions under scrutiny, an accurate comparison matters for buying decisions and policy alike. A converter that handles the inverse relationship and keeps the US and imperial gallons distinct lets a buyer compare a US window sticker, a European spec, and an Asian km/L figure on a true, like-for-like basis.