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Conversionsvehicle

Fuel Economy Converter

Fuel economy across km/l, both mpg conventions and l/100km. The imperial gallon is about twenty percent larger than the US one, so the same car reads noticeably better in UK mpg.

Also called: mpg to kmpl, fuel consumption converter.

km per litre
18

18 kmpl is 18 km/l, 42.34 US mpg, 50.85 imperial mpg or 5.56 l/100km. The imperial gallon is 4.54609 litres against 3.785411784 for the US gallon, about twenty percent larger.

US mpg
42.34
Imperial mpg
50.85
Litres per 100 km
5.56
Miles per litre
11.18
On the two gallons
The imperial gallon is 4.54609 litres against 3.785411784 for the US gallon, about twenty percent larger.
On the two kinds of measure
l/100km measures consumption and mpg measures economy, so they are reciprocals rather than a rescaling.
How this is calculated
Method and background

How this is calculated

Everything converts through kilometres per litre. Two traps: the US and imperial gallons differ, with the imperial about twenty percent larger, so a UK mpg figure is not comparable with a US one for the same vehicle. And l/100km is a consumption measure while mpg is an economy measure, so they are reciprocals. That means the saving from 10 to 15 l/100km is not the same as from 15 to 20, which is why consumption figures make efficiency comparisons more honest than economy figures.

consumption and economy are reciprocals, so a linear improvement in one is not linear in the other
e
Economy

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

18 km per litre

Value
18
From
km per litre

km per litre18

100/18; and 18 x 3.785411784 / 1.609344

Open this example

imperial reads higher than US

Value
40
From
miles per US gallon

km per litre17.01

boundary: the gallon difference, about 20 percent

Open this example

Method and limits

What it assumes

  • Exact conversion factors, with the two gallon definitions kept distinct.

What it deliberately does not model

  • Real economy depends on driving conditions far more than on any conversion.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Why is UK mpg higher than US mpg for the same car?
The imperial gallon is about twenty percent larger than the US gallon, so the same fuel goes further per gallon by definition. The car has not changed.
Why does Europe use l/100km?
It measures consumption rather than economy, which makes savings comparable. Dropping from 10 to 9 l/100km saves the same fuel per distance as 9 to 8, which mpg figures obscure.