MPG to L/100 km Converter (US & UK mpg, km/L)

Understanding the MPG to L/100 km converter — concept and principle

This converter changes fuel economy figures between US miles per gallon, UK miles per gallon, litres per 100 km, kilometres per litre and miles per litre. It helps when comparing cars from different markets, reading foreign reviews or working out fuel costs on a trip abroad.

Distance per fuel ↔ fuel per distance — with the default inputs: 7.84 L/100 km.

How it is calculated

Everything is first converted to km/L: US mpg × 1.609344 ÷ 3.785411784; UK mpg × 1.609344 ÷ 4.54609
L/100 km = 100 ÷ km/L
US mpg = km/L × 3.785411784 ÷ 1.609344; UK mpg = km/L × 4.54609 ÷ 1.609344
Shortcuts: L/100 km = 235.215 ÷ US mpg = 282.481 ÷ UK mpg

Unit definitions are exact: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 UK gallon = 4.54609 L.

The principle

Miles per gallon and kilometres per litre measure distance per unit of fuel: higher is better. Litres per 100 km measures fuel per distance: lower is better. Because one is the reciprocal of the other, the conversion is not linear. The UK (imperial) gallon is about 20% larger than the US gallon, so the same car shows a UK mpg about 20% higher than its US mpg.

Worked example

Default: 30 mpg (US).

km/L = 30 × 1.609344 ÷ 3.785411784 = 12.75.
L/100 km = 100 ÷ 12.754 = 7.84.
UK mpg = 12.754 × 4.54609 ÷ 1.609344 = 36.03.
Miles per litre = 12.754 ÷ 1.609344 = 7.93; US mpg 30.

Each point is the calculator re-run with only “Value” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Value	L/100 km
7.5	31.36
15	15.68
22.5	10.45
30	7.84
37.5	6.27
45	5.23
60	3.92

How to read the result

Because L/100 km is a fuel-per-distance measure, it shows savings directly. Going from 10 to 20 mpg saves far more fuel than going from 30 to 40 mpg over the same distance; in L/100 km the first change is 23.5 → 11.8 and the second only 7.8 → 5.9. Official ratings come from standardised tests and are usually better than real-world results.

Common mistakes

Mixing US and UK mpg figures.
Averaging mpg values over trips of different length; average fuel used per distance instead.
Comparing a test-cycle rating with your own real-world figure.
Thinking higher L/100 km is better.

Keep in mind: Real fuel use depends on driving style, load, weather, tyres and traffic. Use converted figures for comparison, not as a guarantee.

Frequently asked questions

How many L/100 km is 30 mpg?

About 7.84 L/100 km for US mpg, or 9.42 for UK mpg.

Why is UK mpg higher than US mpg for the same car?

The imperial gallon is larger (4.546 L vs 3.785 L), so more miles fit in each gallon.

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

Divide 100 by the km/L figure.

Sources: NIST Special Publication 811 (2008), Appendix B (mile, US gallon, UK gallon)

Checked 9 Nov 2026. Exact unit definitions from NIST SP 811 (2008), Appendix B: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 UK gallon = 4.54609 L.

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