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MPG to L/100 km converter: UK and US gallons

Convert fuel consumption to compare figures in the same unit. Select British or US mpg correctly: the gallons differ. A unit conversion does not make different test conditions equivalent.

Input values

Values are processed in your browser, without sending them to a calculation service or saving them. Reloading clears the form.

Scope and limits

Converting units does not make different test cycles comparable. A laboratory figure and an observed trip consumption can differ for reasons unrelated to the units. This tool does not predict range, fuel prices or electric energy consumption.

How to use the result

Choose the unit used by your source before entering its value. At 40 UK mpg the result is about 7.06 L/100 km; 40 US mpg is about 5.88 L/100 km. Higher mpg is better economy, whereas lower L/100 km is better.

Method and assumptions

A mile is 1.609344 km. A UK gallon is 4.54609 L and a US gallon 3.785411784 L. L/100 km = 100 × litres per gallon ÷ kilometres per mile ÷ mpg. For km/L, L/100 km = 100 ÷ km/L.

Worked example

Input values

Consumption value
40
Consumption unit
Miles per UK gallon

Result of this example

Litres per 100 km
7.06 L/100 km
Miles per UK gallon
40 mpg UK
Miles per US gallon
33.31 mpg US
Kilometres per litre
14.16 km/L

Compare two cars even when the units differ

Put both vehicles on the same distance. The result converts each rating to litres per 100 km before calculating fuel used. Positive savings mean B uses less than A; negative savings mean B uses more.

Your entries stay in this browser tab. Nothing is sent to Osmopark.

Worked example and its assumptions
Vehicle A consumption
40
Vehicle A unit
MPG (UK)
Vehicle B consumption
6
Vehicle B unit
L/100 km
Distance (km)
500
A: L/100 kmB: L/100 kmA: litres for the tripB: litres for the tripLitres saved
7.06635.31305.31

Use comparable test cycles or your own measured figures. Converting WLTP and real-world numbers does not make their measurement conditions identical.

Why an extra 10 MPG does not always save the same fuel

Compare an identical MPG improvement from two starting points. Litres per distance vary with the reciprocal of MPG: the same MPG gain saves more fuel when starting from a thirstier vehicle. Select UK or US gallons explicitly.

Your entries stay in this browser tab. Nothing is sent to Osmopark.

Worked example and its assumptions
Vehicle A consumption
20
Vehicle B consumption
40
Improvement in MPG
10
MPG convention
MPG (US)
Distance (km)
1000
Before (MPG)After (MPG)Before (L/100 km)After (L/100 km)Litres saved
203011.767.8439.2
40505.884.711.76

Sources and review

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