MPG to L/100km converter
Convert UK miles-per-gallon to litres per 100km, or L/100km back to mpg — with the US mpg equivalent — so you can compare UK, European and American fuel-economy figures.
Result
Fuel economy
US equivalent
Result
Fuel economy
US equivalent
How to use this tool
- Choose mpg → L/100km or L/100km → mpg.
- Enter the figure from the spec sheet or review.
- Read the converted figure and the US mpg equivalent.
Assumptions
- UK (imperial) gallon of 4.54609 litres; US gallon of 3.785411784 litres.
- Converts units only — it doesn't adjust for different official test cycles.
Sources & reference data
Technical details: what the fields mean
- Fuel economy
mpg - Miles per UK gallon (4.54609 litres) — the figure normally quoted on UK car specs.
Methodology
L/100km = (100 × 4.54609) ÷ (mpg × 1.609344) ≈ 282.48 ÷ mpg, and mpg ≈ 282.48 ÷ L/100km — the relationship is inverse. US mpg = UK mpg × (3.785 ÷ 4.546) ≈ UK mpg × 0.833, because a US gallon is smaller.
Worked example
45 mpg (UK)
Inputs: Fuel economy: 45 mpg (UK)
Result: 6.28 L/100km, or 37.5 US mpg.
60 mpg (UK) — a frugal diesel or hybrid claim
Inputs: Fuel economy: 60 mpg (UK)
Result: 4.71 L/100km.
L/100km → mpg: a European review quotes 5.0 L/100km
Inputs: Fuel consumption: 5 L/100km
Result: 56.5 mpg (UK), 47.0 US mpg.
L/100km → mpg: 7.5 L/100km
Inputs: Fuel consumption: 7.5 L/100km
Result: 37.7 mpg (UK).
Practical guidance
- Because the scale is inverse, equal mpg gains aren't equal savings: going from 20 to 30 mpg saves far more fuel than 50 to 60 mpg.
- To estimate a trip's fuel cost, use the petrol or diesel journey cost calculators with your mpg figure.
Common mistakes
- Confusing UK and US gallons — US mpg figures are about 17% lower for the same car.
- Treating L/100km like mpg: a lower L/100km figure is better.
FAQs
What is 45 mpg in L/100km?
About 6.28 L/100km.
What is 5 L/100km in mpg?
About 56.5 UK mpg, or 47.0 US mpg.
Why is US mpg lower than UK mpg for the same car?
A US gallon is 3.785 litres, a UK gallon 4.546 litres, so the same car travels fewer miles per (smaller) US gallon.
Last reviewed: 2026-09-24
A unit conversion — it does not adjust for different test cycles (e.g. WLTP vs EPA) behind the original figure.
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