Fuel Economy Converter

Written byOleh Soloninupdated 25 September 2026

Value

Unit

Result

L/100 km8
km per liter12.5
MPG (US)29.402
MPG (UK)35.31

Two gallons, two directions, one honest comparison

Convert MPG to litres per 100 km and back, with US and imperial gallons handled separately. Shows all four figures at once.

Fuel economy is the conversion most likely to mislead, for two reasons. American and British gallons are different sizes, and L/100 km runs backwards to MPG — lower is better on one scale, higher on the other.

Because it is an inverse relationship, you cannot convert it in your head with a simple factor. This page shows L/100 km, km/L, US MPG and imperial MPG together so the comparison is unambiguous.

How to use

Enter a fuel economy figure.
Choose what it is written in: L/100 km, US MPG, UK MPG or km/L.
The calculator shows all four at once — there is no 'to' unit to pick.

L/100 km to MPG

The scales run in opposite directions: fewer litres per 100 km means more miles per gallon. So one litre on an economical car is a lot of MPG and on a thirsty one very little: 4 and 5 L/100 km are 11.8 US MPG apart, 12 and 15 only 3.9.

Every row comes from the calculator on this page.
L/100 km	km/L	US MPG	UK MPG
4	25	58.8	70.62
5	20	47.04	56.5
6	16.67	39.2	47.08
8	12.5	29.4	35.31
10	10	23.52	28.25
12	8.33	19.6	23.54
15	6.67	15.68	18.83

MPG to L/100 km

The US gallon is smaller than the imperial one, so the same MPG figure means different things: 30 US MPG is 7.84 L/100 km, 30 UK MPG is 9.42.

Every row comes from the calculator on this page.
From	L/100 km	km/L
20 US MPG	11.76	8.5
30 US MPG	7.84	12.75
40 US MPG	5.88	17.01
50 US MPG	4.7	21.26
30 UK MPG	9.42	10.62
50 UK MPG	5.65	17.7

What this calculator shows

All four economy figures at once from a single input
US and UK MPG kept separate, since the imperial gallon is 20% larger
km/L for markets that quote distance per litre

What to keep in mind

The US gallon is 3.785 L and the imperial gallon 4.546 L.
Official figures come from standard test cycles; real consumption depends on driving style, roads and weather.

FAQs

Is 30 MPG the same in the US and the UK?

No. 30 US MPG is 7.84 L/100 km, while 30 imperial MPG is 9.42 L/100 km. The British figure describes a noticeably thirstier car.

What is 8 L/100 km in MPG?

29.4 US MPG and 35.3 UK MPG — which is 12.5 km/L.

Why can't I just multiply to convert MPG?

Because the two scales are inverses — distance per fuel versus fuel per distance. You divide a constant by the figure: L/100 km = 235.21 / US MPG.

Which unit is actually more useful?

L/100 km, because it scales linearly with fuel cost. Going from 15 to 14 L/100 km saves more fuel than the MPG scale suggests.

How do I work out my real consumption?

Fill the tank, reset the trip meter, drive normally, then refill. Litres added divided by kilometres travelled, times 100, gives your true L/100 km.

What is km/L?

Kilometres per litre, the unit used in Japan and India. It is the reciprocal of L/100 km: 10 L/100 km is 10 km/L, 5 L/100 km is 20 km/L.

Worked example

A European car quoted in MPG

Input: 8 L/100 km

Output: 29.4 MPG (US) · 35.3 MPG (UK) · 12.5 km/L

Note: The same car looks nearly six MPG thriftier in British adverts purely because the gallon is bigger.

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