Fuel Economy Converter

Convert fuel economy between miles per gallon (US and UK), litres per 100 km and kilometres per litre — with a comparison chart.

How fuel economy conversion works

These units don't scale linearly — MPG and km/L measure distance per fuel while L/100km measures fuel per distance, so converting between the two families requires a reciprocal:

km/L = mpg(US) × 0.425144  ·  km/L = mpg(UK) × 0.354006  ·  km/L = 100 ÷ L/100km

Comparison chart

L/100kmkm/LMPG (US)MPG (UK)
5204756.5
616.739.247.1
812.529.435.3
101023.528.2
156.715.718.8

Worked example

A car rated 8 L/100km: km/L = 100 ÷ 8 = 12.5. In US MPG: 12.5 ÷ 0.425144 ≈ 29.4 MPG; in UK MPG: 12.5 ÷ 0.354006 ≈ 35.3 MPG.

Frequently asked questions

How do I convert MPG to L/100km?
For US gallons: L/100km = 235.215 ÷ mpg. For UK (imperial) gallons: L/100km = 282.481 ÷ mpg. Note the inversion — higher MPG means LOWER litres per 100 km.
Why are US and UK MPG different?
The gallons differ: a US gallon is 3.785 litres, an imperial (UK) gallon is 4.546 litres. The same car scores about 20% higher in UK MPG than US MPG.
Is 8 L/100km good fuel economy?
8 L/100km (about 29 US MPG / 35 UK MPG) is typical for a mid-size petrol car. Small efficient cars manage 5–6 L/100km; SUVs and older vehicles often use 10–15.
Why can’t I just multiply by a constant?
Because MPG and L/100km are reciprocals of each other — one measures distance per fuel, the other fuel per distance. Doubling MPG halves L/100km, so the conversion divides rather than multiplies.

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