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

What this converter does

UK fuel economy is quoted in miles per Imperial gallon, while much of the world uses kilometres per litre. This converter takes a UK mpg figure and turns it into km/L. Enter the mpg value and read off the km/L, so a British economy figure can be read in metric terms.

The conversion factor

To go from UK mpg to kilometres per litre you multiply:

km/L = mpg (UK) × 0.354006

That single factor combines miles into kilometres and UK gallons into litres. Notice it is a smaller number than the one used for US mpg, and that is entirely down to the gallon, which is the key thing to get right here.

Why this uses the UK gallon

A UK gallon, the Imperial one, is about 4.546 litres, noticeably bigger than the US gallon's 3.785 litres. Because a UK mpg figure is already measured against that larger gallon, converting it to km/L uses a different factor from the US version. The practical point is simple: make sure you know whether your mpg figure is UK or US before you convert, because using the wrong factor will throw the answer off by around 20 percent. A figure labelled just "mpg" in a British source is almost always the Imperial one.

A worked example

Say a car is rated at 45 mpg in the UK and you want that in kilometres per litre.

• 45 × 0.354006 = 15.9 km/L

So 45 UK mpg is about 15.9 km/L. In a market that quotes km/L, that is a solidly economical figure, the kind of number a careful small petrol car or a frugal diesel would post.

Common mpg (UK) values in km/L

As anchors, 40 mpg UK is about 14.16 km/L, and a frugal 60 mpg UK comes out near 21 km/L.

Where it helps

This is for taking a British economy figure into a metric setting. Markets that quote km/L, common across Asia, use a measure a UK figure does not match directly, so converting lets you compare like with like. It helps when looking at a model sold in several countries, when reading a metric review, or when lining a UK-rated car up against locally quoted ones. The main thing is simply to start from a genuine UK mpg figure, since the Imperial gallon is what this factor is built around.

Questions people ask

How do I convert UK mpg to km/L?

Multiply the UK mpg figure by 0.354006. The factor combines the mile-to-kilometre and UK-gallon-to-litre conversions.

Why is the factor different from the US one?

Because the UK gallon is larger than the US gallon. A UK mpg figure is measured against that bigger gallon, so it converts to km/L with a different factor.

What is 45 UK mpg in km/L?

About 15.9 km/L, a solidly economical figure for a small petrol car or a frugal diesel.

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