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Fuel Efficiency Converter

Fuel economy travels in three directions: kilometres per litre in much of the world, miles per gallon in the United States and the United Kingdom — with different gallons — and litres per 100 km in Europe. The last one runs backwards: a car drinking 6.5 L/100 km is efficient, not thirsty. This converter takes any of the three and returns the others, so a listing from another continent still makes sense.

Enter values

From a fuel log, a spec sheet or a trip computer

Kilometres per litre globally, mpg in the UK and US

Results update as you type.

Results

In MPG (US)
23.5215
In litres per 100 km (L/100 km)
10
In MPG (UK)
28.2481
Exact factor
1 km/L = 2.352146 mpg (US)

How is the Fuel Efficiency Converter calculated?

Enter a fuel figure, choose whether it is km/L, MPG (US) or MPG (UK), and read the answer. The headline result is your chosen unit; the rows beneath show kilometres per litre, both gallon standards and the extra litres per 100 km row this converter computes for you. Zero is handled honestly: any reciprocal of zero is undefined, so the page shows an em dash rather than inventing a number.

Formula

Fuel figures convert through kilometres per litre: km/L = value × from-unit factor, then target = km/L ÷ to-unit factor. The gallon factors are 1 km/L = 2.352145833 mpg (US) and 1 km/L = 2.824809363 mpg (UK), stored reciprocally so the arithmetic lands on the right side. Litres per 100 km is 100 ÷ km/L, the pure reciprocal of the metric scale.

Example

A compact car returning 10 km/L is drinking 10 L per 100 km and covers 23.52 miles on a US gallon, or 28.25 on a UK one. An American hatchback at 25 mpg (US) achieves 10.63 km/L, which Europeans would list as 9.41 L/100 km. A European 6.5 L/100 km estate manages 15.38 km/L and 36.19 mpg across the Atlantic, while 40 mpg (UK) is 14.16 km/L or 33.31 mpg (US) — the same car, two marketing figures.

Things to remember

Every fuel scale measures the same journey, so the honest comparison is the one you can flip in either direction. Remember the direction of travel: bigger is better for miles and kilometres per litre, smaller is better for litres per 100 km — and the UK gallon is 20% larger than the US one.

Frequently Asked Questions

How do I convert litres per 100 km to MPG?

Divide 235.2145833 by the L/100 km figure for US gallons, or 282.4809363 for UK gallons. A car using 9 L/100 km therefore returns 235.2145833 ÷ 9 = 26.13 mpg (US), or 31.39 mpg (UK). The lower the L/100 km number, the higher the MPG.

Are UK and US miles per gallon really different?

Yes — by about 20%, because the imperial gallon holds 4.54609 litres and the US gallon 3.785411784. A UK 40 mpg rating is 33.31 mpg on the US scale, so comparing figures across the Atlantic without converting makes a car look better than it is.

Why do European cars quote litres per 100 km?

Because it describes fuel consumed rather than distance covered, which makes fleet budgets easy to total. Filling 45 litres into a 6.5 L/100 km car covers about 692 km. It also reverses the usual intuition: the smaller the number, the more efficient the vehicle.

What is the easiest way to compare two fuel ratings?

Pick one scale and convert the other into it. A quick mental check uses kilometres per litre: 7 L/100 km is about 14.3 km/L, and multiplying by 2.352145833 gives roughly 33.6 mpg (US). Anything above 14 km/L is a genuinely economical petrol car.

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