Fuel Economy Converter (mpg US/UK, km/L, L/100km)
Type a fuel economy value and select its unit; see equivalents in all four major systems instantly. Important when comparing US and European vehicle specs.
How it works
Why mpg is bigger in the UK
1 UK / imperial gallon is 4.5461 L; the US gallon is only 3.7854 L. So a car running at 30 mpg in the UK uses one gallon (4.55 L) per 30 miles; a 30 mpg US car uses one gallon (3.79 L) per 30 miles. The UK car is going further per liter — UK mpg numbers look better for the same vehicle. Multiply UK mpg by 0.8327 to get US mpg.
This is the most common cross-Atlantic confusion in car reviews. When you see a UK auto magazine quoting 50 mpg, that's about 42 mpg in US terms — and roughly 5.6 L/100km.
L/100km vs mpg — they're inverted
L/100km is fuel used per fixed distance. Smaller is better. Most of Europe and Japan use this.
mpg is distance traveled per fixed fuel. Bigger is better. The US, UK, and Canada use this.
Because of the inversion, equal-percent improvements look very different. Going from 6 to 5 L/100km is a 17% efficiency gain — but going from 39 to 47 mpg (the equivalents) is a 21% gain by mpg math. Always compare on the same metric.
Quick reference
30 mpg (US) ≈ 36 mpg (UK) ≈ 12.75 km/L ≈ 7.84 L/100km. 50 mpg (US) ≈ 60 mpg (UK) ≈ 21.25 km/L ≈ 4.7 L/100km. A modern compact ICE car gets ~30-40 mpg US / 6-8 L/100km. Hybrids get 50+ mpg US / under 5 L/100km. EVs use kWh/100km or kWh/mi instead — different metric entirely.
Frequently asked questions
›How do I convert mpg to L/100km?
L/100km = 235.215 / mpg (US) or 282.481 / mpg (UK). The calculator does this automatically once you pick the right gallon.
›Why does L/100km go down when efficiency goes up?
Because it's 'fuel per distance'. Less fuel for the same 100 km = more efficient. Don't be fooled — smaller numbers are better.
›Is UK mpg the same as Imperial mpg?
Yes — UK and Imperial are interchangeable terms for the same gallon (4.5461 L).
›What about Australia and Canada?
Australia uses L/100km (metric). Canada displays both L/100km and mpg, but the mpg is now imperial (UK), not US — same word, different gallon.
›Are these conversions exact?
Yes. Mile, gallon, and liter are all exact rational definitions (1 mile = 1.609344 km exactly, etc.).
›How do EVs fit in?
EV efficiency is electric energy per distance — kWh/100km or miles/kWh. The 'mpge' label converts that to a gasoline-equivalent for comparison, but the underlying math is different.
›Why do real-world numbers differ from EPA / WLTP?
Test cycles use specific speeds and driving profiles. Real driving with hills, traffic, and aggressive acceleration is typically 10-20% worse than the rated number.
›Does the data leave my browser?
No. Conversion runs locally.
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