This fuel economy converter translates between the world’s fuel-economy dialects: US MPG, UK MPG, L/100 km and km/L — including the trap that two of them run backwards.

The reciprocal relationship: L/100km = 235.215 ÷ MPG(US) — consumption and economy are inverses, so doubling MPG halves L/100km, and the same +5 MPG means wildly different savings at 15 MPG vs 45 MPG (the “MPG illusion” regulators keep warning about).

Two Gallons, Two Directions, One Constant: 235.215

The US gallon (3.785 L) and Imperial gallon (4.546 L) differ by 20%, so “30 MPG” is two different cars depending on the ocean. Computing MPG from your own fill-ups is our MPG Calculator. Part of our Conversion Calculators collection.

Anchor Conversions (Verified)

  • 30 MPG (US) = 7.84 L/100 km = 12.75 km/L = 36.0 MPG (UK) — the defaults, fully translated
  • The gas-guzzler anchor: 15 MPG US = 15.68 L/100 km; the hybrid anchor: 50 MPG US = 4.70 L/100 km
  • European window stickers lead with L/100 km (lower = better); North America leads with MPG (higher = better) — comparison shoppers must flip both the number and the instinct
  • EVs join via MPGe and kWh/100 mi — different fuel, same reciprocal grammar

The MPG Illusion, Quantified

  • Trading 15 → 20 MPG saves ≈ 167 gallons per 10,000 miles (667 → 500 gal); trading 40 → 45 MPG saves only ≈ 28 gallons (250 → 222 gal). L/100 km spacing makes the gallons honest at a glance.
  • Fleets and regulators increasingly think in consumption (fuel per distance) for exactly this reason.
  • UK MPG flatters by 20% on identical cars — imported reviews need the converter before the envy.

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Frequently Asked Questions

How do I convert MPG to L/100km?

Divide 235.215 by the US MPG: 30 MPG → 7.84 L/100 km. For UK MPG, divide 282.481 instead. The relationship is reciprocal, not proportional — this converter handles all four units both directions.

Why are US and UK MPG different?

The gallons differ: US gallon = 3.785 L; Imperial gallon = 4.546 L (20% more fuel per “gallon”), so the same car posts a 20% higher UK MPG. 30 MPG US = 36.0 MPG UK for identical real-world consumption.

Is higher or lower L/100km better?

Lower. L/100 km measures consumption (fuel burned per distance), while MPG measures economy (distance per fuel). The best cars sit near 4–5 L/100 km (47–59 MPG US); heavy SUVs run 12–16 L/100 km (15–20 MPG).

What is km/L?

Kilometres per litre — the MPG-style (distance-per-fuel) metric used in much of Asia and Latin America. km/L = 100 ÷ L/100 km, and MPG(US) ≈ km/L × 2.352. The defaults’ 12.75 km/L equals 30 MPG US.

Why do regulators dislike MPG?

The MPG illusion: equal MPG gains save unequal fuel (15→20 MPG saves 167 gal/10k mi; 40→45 saves 28). Consumption units (L/100 km, gal/100 mi) space savings linearly, which is why policy and engineering increasingly quote them.

Is this fuel economy converter free?

Yes — free, instant, no sign-up.