MPG (US) to MPG (UK) Converter
Quickly convert from MPG (US) to MPG (UK).
How to convert
Formula:
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Measures the economy of a vehicle — how much fuel it needs to cover a distance.
Where is it used?
In the automotive industry for comparing vehicles. In Europe we measure L/100km, while in the US/UK MPG (miles per gallon).
Examples:
• An economical car burns 4-5 L/100km.
• 15 km/L corresponds to about 6.6 L/100km.
• The lower the L/100km, the more economical the vehicle.
Fuel economy units vary by country in ways that can be deeply confusing — and the logic is often inverted. Miles per gallon (MPG) rewards higher numbers, while liters per 100 km (L/100km) rewards lower ones. Understanding these conversions is essential for comparing vehicles, planning road trips, and making informed purchasing decisions across borders.
Fuel economy (or fuel efficiency) measures how far a vehicle travels per unit of fuel — or how much fuel it uses to cover a given distance. The three main systems are: MPG (US and UK, miles per gallon — higher = more efficient), L/100km (most of Europe, Asia — lower = more efficient), and km/L (Japan, India, Latin America — higher = more efficient). The US and UK gallon are different, making MPG comparisons tricky across those two countries.
Where is it used?
- Automotive industry — Vehicle fuel economy ratings in regulatory filings and advertising.
- Car buying — Comparing fuel costs between models across different countries.
- Road trip planning — Calculating fuel stops and costs on long journeys.
- Emissions regulations — Fleet average fuel economy standards (CAFE in the US, CO₂ g/km in Europe).
- Aviation & Shipping — Fuel burn in liters per hour or kg per nautical mile for aircraft.
Common Conversion Mistakes
Comparing US MPG with UK MPG directly
A US gallon = 3.785 L; a UK gallon = 4.546 L. A car rated at 40 MPG (UK) is NOT as efficient as one rated 40 MPG (US) — the UK car is actually more efficient (uses less fuel per mile) because its gallon is larger. 40 MPG UK ≈ 33 MPG US.
Assuming better MPG is always better
L/100km uses inverse logic: lower is better. A car using 5 L/100km is more efficient than one using 8 L/100km. The difference between 5 and 6 L/100km saves more fuel than the difference between 15 and 16 L/100km — the relationship is nonlinear.
Ignoring the inverse relationship in MPG improvements
Going from 15 to 20 MPG saves more fuel than going from 40 to 50 MPG (over the same distance). Improving a gas-guzzler by 5 MPG saves more than improving an efficient car by 10 MPG. This counterintuitive fact is called the 'MPG illusion'.
Not converting when comparing international car reviews
European car reviews quote L/100km; US reviews use MPG. A European car at 6.5 L/100km sounds very different from its equivalent 36.2 MPG. Always convert when comparing vehicles reviewed in different markets.
Quick Reference Table
| From | To |
|---|---|
| 10 L/100km | 23.5 MPG (US) |
| 7 L/100km | 33.6 MPG (US) |
| 5 L/100km | 47.0 MPG (US) |
| 30 MPG (US) | 7.84 L/100km |
| 40 MPG (US) | 5.88 L/100km |
| 40 MPG (UK) | 33.2 MPG (US) |
| 15 km/L | 6.67 L/100km |
| 1 MPG (US) | 0.4251 km/L |
Frequently Asked Questions
How do I convert MPG to L/100km?
Use the formula: L/100km = 235.21 ÷ MPG (US). For example, 30 MPG US = 235.21 ÷ 30 = 7.84 L/100km. The constant 235.21 comes from the conversion factors for miles-to-km and US gallons-to-liters. Going the other way: MPG (US) = 235.21 ÷ L/100km.
What is a 'good' fuel economy for a car?
This varies by vehicle type. For passenger cars: under 6 L/100km (>39 MPG US) is excellent; 6-9 L/100km (26-39 MPG) is good; 9-12 L/100km (20-26 MPG) is average; over 12 L/100km (<20 MPG) is poor. Hybrid cars typically achieve 4-6 L/100km; full EVs are rated in equivalent MPG (MPGe) — often 100+ MPGe.
Why is L/100km better than MPG for comparing cars?
L/100km has a linear relationship with fuel consumption — using 1 L/100km less always saves the same amount of fuel per 100 km driven. MPG has an inverse (nonlinear) relationship. Going from 15 to 18 MPG saves much more fuel than going from 40 to 43 MPG. The 'MPG illusion' makes people systematically undervalue improvements in low-MPG vehicles.
What is the difference between US and UK gallons?
A US liquid gallon = 3.785 liters. A UK (imperial) gallon = 4.546 liters. The UK gallon is about 20% larger. This means UK MPG figures are consistently higher than US MPG for the same vehicle — a car rated 35 MPG (UK) is equivalent to about 29 MPG (US).
How does fuel economy affect running costs?
Over 15,000 km per year with fuel at $1.50/L: a car doing 6 L/100km costs $1,350/year in fuel; one doing 10 L/100km costs $2,250/year — $900 more. Over 5 years, that's $4,500 difference in fuel alone, often exceeding the premium for a more fuel-efficient model.
Sources & Standards
- US Environmental Protection Agency (EPA) — fueleconomy.gov
- European Environment Agency (EEA)
- International Energy Agency (IEA)
Reviewed by The Unit Hub Editorial Team · March 2026