Fuel Economy Converter
MPG (US & UK), L/100km and km/L — plus your real consumption from a trip.
About this converter
Type in any box — US MPG, UK MPG, L/100km, km/L — and the others follow, with a plain-language verdict on what the number means. The trip section computes your REAL consumption from distance and litres at a fill-up, which is the only figure that never lies.
Two gallons, opposite scales, honest numbers
The traps this converter exists for: US and UK gallons differ by 20% (3.785 vs 4.546 litres — the 1824 split), so "40 MPG" is two different cars depending on the accent; and the scales run opposite directions — big MPG good, big L/100km bad — which breaks mental comparison. Anchors: 40 MPG(US) ≈ 5.9 L/100km ≈ 17 km/L; hybrids live under 4.5 L/100km. The measured-versus-brochure gap is real and normal: official cycles are gentler than traffic, so expect 10–20% worse — measure with the fill-to-fill method (brim the tank, zero the trip, drive, brim again) for your honest number. What the consumption costs in money per trip is the fuel cost calculator's job.
Frequently asked questions
What is 40 MPG in litres per 100 km?
US MPG: 5.9 L/100km. UK MPG: 7.1 L/100km — the gallons differ by 20%, which is exactly why this converter labels them separately.
Why do MPG and L/100km run opposite ways?
MPG measures distance per fuel (bigger = better); L/100km measures fuel per distance (smaller = better). Same information, inverted — and the inversion defeats head math, hence the tool.
How do I measure my car's real consumption?
Fill to the brim, zero the trip meter, drive normally, fill to the brim again: litres of the second fill ÷ trip distance × 100 is your true L/100km. The trip section does the arithmetic.
Why is my consumption worse than the brochure?
Official test cycles are gentler than real traffic — 10-20% worse on the road is normal and not a fault. Cold starts, short trips and roof racks widen the gap.