Fuel Economy Converter (MPG ⇄ L/100km)
The same car can be quoted as 14 km/L in Hong Kong or Japan, 7.1 L/100km in Europe, 33 MPG in the US and 40 MPG in the UK — all describing the identical fuel use. Enter any one figure and this tool lays out all four common units side-by-side, so you can read foreign car magazines, compare grey-import specs and fill in emissions paperwork without converting in your head.
Please enter a fuel-economy value greater than 0.
All four units at a glance
- L/100km
- —
- km/L
- —
- MPG (US)
- —
- MPG (UK imperial)
- —
Lower L/100km is more efficient; higher km/L and MPG are more efficient. JDM/EU specs usually quote L/100km or km/L; US/UK specs quote MPG.
Formula
km/L = 100 / (L/100km); MPG (US) = km/L × (3.785 411 784 / 1.609 344); MPG (UK) = km/L × (4.546 09 / 1.609 344).
- · 1 US gallon = 3.785 411 784 L; 1 UK (imperial) gallon = 4.546 09 L (NIST exact values).
- · 1 mile = 1.609 344 km (international yard-and-pound agreement, 1959, exact).
- · L/100km is "fuel used" (lower is better); km/L and MPG are "distance covered" (higher is better) — so L/100km is the reciprocal of km/L, not a linear conversion.
- · US and UK MPG differ by ~20 %: the imperial gallon is about 20 % larger, so the same car always reads as a bigger MPG number in UK units. Quick rule: MPG (UK) ≈ MPG (US) × 1.2.
- · Typical petrol passenger car: 6–9 L/100km (≈ 26–39 MPG US). Compact hybrid: 4–5 L/100km. Diesel SUV: 8–10 L/100km. Classic American V8: 14–20 L/100km.
- · This tool only converts the rating between units; for the cost of an actual trip use the Fuel Cost Calculator.
- · Sources: NIST SP 811 (Appendix B), BIPM SI Brochure 9th ed., U.S. EPA fueleconomy.gov conversion tables.
Frequently asked
Why are US and UK MPG figures so different for the same car?
The two countries use different gallons. A US gallon is 3.785 L; a UK (imperial) gallon is 4.546 L — about 20 % larger. So a car that burns 7 L per 100 km is roughly 33.6 MPG in the US and 40.4 MPG in the UK — the gap is purely a unit artefact, not an efficiency difference. When you read English car magazines, check which market the figure is quoted in before comparing.
Is L/100km or km/L the better way to express fuel economy?
L/100km is more intuitive for day-to-day planning: you know roughly how much fuel you put in and how far you drive, and a simple division tells you when to refuel next. It also has higher resolution at the efficient end — 8 vs 7 L/100km is easier to feel than 12.5 vs 14.3 km/L. km/L, on the other hand, naturally answers "how far does one litre take me?" which is useful for trip planning. Europe, Hong Kong, Japan and Australia all mix the two; the right unit is whichever matches your mental model.
My car is rated at 6.5 L/100km but I actually get about 8 — is something wrong?
Almost always normal. Factory figures come from standardised laboratory cycles (WLTP, NEDC or EPA) under ideal temperature, speed, load and acceleration profiles. Real-world use commonly adds 20–30 % to consumption, especially with short trips, heavy traffic, full air-conditioning, extra payload, low tyre pressure, larger wheels or hilly terrain. If you are seeing more than 50 % worse than the sticker and your driving style hasn’t changed, it is worth checking the air filter, spark plugs, tyre pressure and the O₂ sensor.
Do electric cars have an equivalent unit? Does this tool convert them?
EVs use kWh/100km, km/kWh or (in the US) MPGe — gallon-of-gasoline-equivalent — which describe a different physical quantity (electricity instead of fuel) and cannot be directly interchanged. This tool focuses on the four common combustion-engine units only. If you want to compare a petrol car against an EV, convert both to MJ/km or kWh/100km on an energy-content basis.
Why is the L/100km unit normalised to 100 km in particular?
Purely for readable numbers. Typical cars burn somewhere between 4 and 15 litres per 100 km, which fits neatly into one- or two-digit values. L/km would give awkward decimals like 0.04–0.15; L/1000km would be unnecessarily large. European industry settled on L/100km early on and ECE regulations together with ISO 4030 adopted it as the official fuel-economy reporting unit.
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