Miles per Gallon (UK) to Liters per 100 Kilometers Converter | mpg (UK) to L/100km

What this converter does

The UK quotes fuel economy in miles per Imperial gallon, while the rest of Europe uses litres per 100 kilometres. This converter takes a UK mpg figure and turns it into L/100km. Enter the mpg value and read off the L/100km, so a British economy figure can be read the continental way.

From UK mpg to the European measure

This is a conversion British drivers reach for often, because the UK sits among neighbours who all use a different measure. Beyond the change of units, there is a change of direction to keep in mind. UK mpg counts distance per gallon, where higher is better. Litres per 100 km counts fuel per distance, where lower is better. So a high UK mpg becomes a low L/100km. Crossing the Channel, in effect, means turning the economy figure over as well as swapping gallons for litres.

The rule and its constant

Because the measures run opposite ways, the conversion is a division:

L/100km = 282.481 ÷ mpg (UK)

That constant, 282.481, bundles the unit change and the reciprocal into one step. It is built on the UK gallon of about 4.546 litres, so it applies only to UK mpg. Divide 282.481 by the mpg figure and you have the L/100km.

A worked example

Say a car is rated at 50 mpg in the UK and you want that in litres per 100 km.

• 282.481 ÷ 50 = 5.65 L/100km

So 50 UK mpg is about 5.65 L/100km. On a European spec sheet that is a frugal car, the sort of figure a careful small petrol or a diesel would post, and now it sits on the same scale as the cars it would be parked beside on the continent.

Common mpg (UK) values in L/100km

As anchors, 40 mpg UK is about 7.06 L/100km, and a frugal 60 mpg UK comes out near 4.7 L/100km.

Why the constant is larger than the US one

If you have seen the US version of this conversion, you will notice its constant is 235.215 while this one is 282.481. The difference is the gallon. A UK gallon is bigger than a US gallon, so a UK mpg figure already represents more fuel and more distance, and the constant has to be larger to land on the right L/100km. The practical takeaway is the usual one with mpg: always know whether a figure is UK or US before converting, because using the wrong constant throws the result off by around 20 percent.

Questions people ask

How do I convert UK mpg to L/100km?

Divide 282.481 by the UK mpg figure. The conversion is a division because the two measures run in opposite directions.

Why is the constant different from the US one?

The UK gallon is larger than the US gallon, so UK mpg uses a constant of 282.481 rather than the 235.215 used for US mpg.

What is 50 UK mpg in L/100km?

About 5.65 L/100km, a frugal figure on a European spec sheet.

References

1. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (gallon definitions and unit conversions). https://www.nist.gov/pml/special-publication-811