Fuel economy is quoted differently around the world: the US uses miles per US gallon, the UK uses miles per imperial gallon, Europe uses litres per 100 km, and several markets use kilometres per litre. Economy figures (higher = better) and consumption figures (lower = better) are reciprocals, so this converter routes every value through L/100km to keep the maths honest.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: US gal = 3.785412 L, imp gal = 4.546090 L, mile = 1.609344 km, recomputed in code.
The conversion constants
235.215 comes from (3.785412 L/gal × 100 km) ÷ 1.609344 km/mile; the UK constant 282.481 uses the larger 4.546090 L imperial gallon. Each relationship is a division because the two sides are reciprocals. To convert between any two units, the tool first turns the input into L/100km, then turns that into the target unit.
Worked examples
30 US MPG to L/100km and km/L:
8 L/100km the other way:
So a car rated 30 US MPG consumes 7.84 L/100km — and the same 8 L/100km reads as 29.40 US MPG but 35.31 UK MPG because the imperial gallon is larger.
Frequently Asked Questions
Divide 235.215 by US MPG (282.481 for UK MPG). 235.215 ÷ 30 = 7.84 L/100km. It's a division — they're reciprocals.
MPG and km/L are distance-per-fuel; L/100km is fuel-per-distance. They're inverse, so you divide a constant by the value.
No. Imperial gallon (4.546 L) is ~20% bigger than US gallon (3.785 L), so 30 UK MPG beats 30 US MPG.
Divide 100 by km/L. 100 ÷ 15 = 6.67 L/100km. Same form in reverse.
Higher MPG and km/L, or lower L/100km. Convert both cars to one unit before comparing.