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Fuel Economy Converter

Converters · Added 15 August 2026

Convert fuel economy between miles per gallon, litres per 100 kilometres, kilometres per litre and miles per litre. Two things trip people up here and both are handled: US and imperial gallons are different sizes, and consumption figures are the reciprocal of economy figures rather than a simple multiple of them.

Result

1 mpg (US) in litres per 100 km

235.214583 L/100km

These units are reciprocals, so the conversion is a division rather than a fixed multiplier — doubling one does not double the other.

The same value in every unit

Litres per 100 km (L/100km)
235.214583
US gallons per 100 miles (gal/100mi)
100
Kilometres per litre (km/L)
0.425143707
Miles per gallon (US) (mpg (US))
1
Miles per gallon (imperial) (mpg (UK))
1.20094993
Miles per litre (mi/L)
0.264172052

US and imperial gallons are different sizes, so “30 mpg” means two different things depending on which side of the Atlantic the figure came from — an imperial gallon is about 20% larger, which makes UK mpg figures look correspondingly better for the identical car. Note also that zero has no reciprocal: a car covering no distance per litre has no finite L/100km.

How to use the fuel economy converter

  1. 1Enter the fuel economy figure you have.
  2. 2Pick the unit it is in — check whether an mpg figure is US or imperial, because they differ by about 20%.
  3. 3Choose the unit you want. The result updates as you type.
  4. 4The table below shows the same economy expressed in every supported unit at once.
  5. 5Use the swap button to reverse the direction.

Examples

A US car in European units

Input
30 mpg (US)
Result
7.84 L/100km · 12.75 km/L

The same car advertised in the UK would be quoted as about 36 mpg, because an imperial gallon is larger.

A European car in US units

Input
5 L/100km
Result
47.04 mpg (US) · 56.5 mpg (UK)

A typical efficient diesel. The gap between the two mpg figures is the gallon difference, not a difference in the car.

Indian fuel economy

Input
18 km/L
Result
5.56 L/100km · 42.3 mpg (US)

Kilometres per litre is the usual measure in India and Japan.

About the fuel economy converter

Two ways of saying the same thing, upside down

Fuel economy figures come in two families that look interchangeable and behave very differently. Distance-per-volume — miles per gallon, kilometres per litre — goes up as a car gets more efficient. Volume-per-distance — litres per 100 km, gallons per 100 miles — goes down. They describe the identical physical fact, and each is the reciprocal of the other.

That reciprocal relationship is why a conversion here is a division rather than a multiplication, and why the usual mental shortcuts fail. If 1 mpg is 235 L/100km, it is tempting to assume 2 mpg is 470. It is not; it is 118. Any conversion factor quoted for this family applies to exactly one value and no others.

It also explains a persistent piece of consumer confusion. Because mpg is a reciprocal scale, equal steps in mpg are not equal savings in fuel. The difference between 10 and 15 mpg is a far larger real saving than the difference between 40 and 45 mpg, which is counterintuitive when both are described as five miles per gallon.

Why the same car has two different mpg figures

The gallon was never standardised across the Atlantic. The US gallon derives from the old English wine gallon of 231 cubic inches; Britain redefined its gallon in 1824 as the volume of ten pounds of water, which came out at 4.54609 litres. The US kept the older, smaller measure. Neither is more correct, and both are still in daily use.

The practical consequence is that an unlabelled mpg figure is ambiguous by about 20%. A car review quoting 40 mpg is describing a substantially more efficient vehicle if the review is British than if it is American. When comparing figures from different sources, the unit label matters as much as the number, and this converter lists the two separately for that reason.

Official test figures add a second layer of incomparability on top of the units. The US EPA cycle, the older European NEDC and the newer WLTP procedure all produce different numbers for the same car, and none of them is what you will see in traffic. Converting a WLTP figure into US mpg gives you a correctly converted number from a test the US does not use — the arithmetic is exact, the comparison is still not like for like.

Frequently asked questions

Why do UK and US mpg figures differ for the same car?
Because the gallons are different. An imperial gallon is 4.54609 litres and a US gallon is 3.785411784 litres — about 20% smaller. A car covering 30 miles on a US gallon covers roughly 36 miles on the larger imperial gallon, so it is quoted as 36 mpg in the UK and 30 mpg in the US without anything about the car changing. Always check which gallon a figure refers to before comparing two cars.
Why can't I just multiply to convert mpg to L/100km?
Because they measure opposite things. Miles per gallon is distance divided by fuel; litres per 100 km is fuel divided by distance. One is the reciprocal of the other, so the conversion is a division: L/100km = 235.215 ÷ mpg(US). That also means the relationship is not linear — going from 20 to 30 mpg saves far more fuel than going from 40 to 50 mpg, even though both are a ten-mpg improvement.
Which figure is better to compare cars with?
Litres per 100 km, or gallons per 100 miles, because consumption scales linearly with fuel used. Improving from 15 to 20 mpg saves about 1.7 gallons per 100 miles; improving from 40 to 50 mpg saves about half a gallon. Quoted in mpg those look like a 5 and a 10 mpg gain respectively, which inverts the truth about which change matters more. This is precisely why the US EPA added a gallons-per-100-miles figure to window stickers.
Why does entering zero give no answer?
Zero has no reciprocal. A vehicle covering zero kilometres per litre would need infinite litres per 100 km, which is not a number the converter can display. Enter any positive figure and it converts normally.

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