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Fuel Economy Converter

Convert fuel economy between US mpg, UK mpg, kilometers per liter, liters per 100 km and miles per liter. Enter one value and see all units at once.

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Convert fuel economy
Must be greater than zero.

Read the guide How to Convert MPG to L/100 km (and Back)

How to use the converter

Enter a fuel economy figure in the Value box, choose its unit and press Convert. The result shows the same figure in every other unit at once: US miles per gallon, UK miles per gallon, kilometers per liter, liters per 100 kilometers and miles per liter. The value must be greater than zero.

Why L/100 km works the other way round

Miles per gallon, kilometers per liter and miles per liter measure distance per fuel: a higher number means a more efficient car. Liters per 100 kilometers measures fuel per distance: a lower number is better. Because one is the reciprocal of the other, converting between them is a division, not a multiplication:

  • L/100 km = 100 ÷ (km/L)
  • L/100 km = 235.215 ÷ mpg (US)
  • L/100 km = 282.481 ÷ mpg (UK)

This also explains why mpg figures can mislead. Over 100 miles, a car that improves from 10 to 20 mpg goes from 10 gallons to 5 and saves 5 gallons. A car that improves from 30 to 40 mpg goes from about 3.33 gallons to 2.5 and saves only about 0.83 gallons. The same 10 mpg gain is worth much more at the low end. Fuel-per-distance units such as L/100 km show the actual fuel saved directly.

US and UK gallons are different

A US gallon is exactly 3.785411784 liters, while a UK (imperial) gallon is exactly 4.54609 liters, about 20% larger. A mile is 1.609344 km in both countries. So the same car shows a higher mpg figure in the UK than in the US: multiply US mpg by about 1.201 to get UK mpg. Always check which gallon a figure uses before comparing cars.

Worked examples

  • 30 mpg (US) = 30 × 1.609344 ÷ 3.785411784 ≈ 12.75 km/L. That gives 100 ÷ 12.75 ≈ 7.84 L/100 km. In UK gallons the same car does about 36.03 mpg, and in miles per liter about 7.93.
  • 6 L/100 km = 100 ÷ 6 ≈ 16.67 km/L, which is about 39.20 mpg (US) or 47.08 mpg (UK).
  • 40 mpg (UK) is about 33.31 mpg (US) or 7.06 L/100 km.
  • 15 km/L is about 6.67 L/100 km.

Good to know

  • Results are rounded to two decimal places; values below 0.1 are shown to three significant digits.
  • Official ratings come from standard test cycles that differ between regions, so a car's US, European and UK figures may not convert exactly into each other even after unit conversion.
  • To estimate the cost of a trip from these figures, use a fuel cost calculator.

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. For example, 30 mpg (US) is 235.215 ÷ 30 ≈ 7.84 L/100 km. The same formula works in reverse: 235.215 ÷ L/100 km gives US mpg.

Why is a lower L/100 km number better?

L/100 km tells you how much fuel the car uses to travel a fixed distance. Using less fuel for the same 100 km is more efficient, so lower is better. For mpg and km/L, which measure distance per unit of fuel, higher is better.

Why do UK mpg figures look higher than US figures?

The UK imperial gallon (4.54609 L) is about 20% larger than the US gallon (3.785411784 L), so a car travels farther on one UK gallon. One US mpg equals about 1.201 UK mpg.

Can I enter zero or a negative value?

No. Fuel economy must be greater than zero: zero distance per liter or zero liters per 100 km would mean the car either never moves or uses no fuel, and the conversion would require dividing by zero.