About the Fuel Economy Converter
Different countries describe fuel economy in different — and not interchangeable — ways. The US uses miles per gallon (US gallon). The UK uses miles per gallon (Imperial gallon, which is bigger). Most of the rest of the world uses litres per 100 km — a consumption metric where lower is better, instead of efficiency where higher is better. Use this tool when comparing a new car spec sheet against your current car, when reading European reviews of American cars (or vice versa), or when planning a road trip across borders.
How to use it
- Pick the unit your current figure is in (MPG-US, MPG-UK, L/100km, or km/L).
- Pick the unit you want.
- Type the value — the converted figure appears immediately.
- Remember that L/100km and MPG move in opposite directions: lower L/100km = better, higher MPG = better.
Common fuel economy conversions
| 20 MPG (US) | 11.76 L/100km |
| 30 MPG (US) | 7.84 L/100km |
| 40 MPG (US) | 5.88 L/100km |
| 50 MPG (US) | 4.70 L/100km |
| 20 MPG (UK) | 14.13 L/100km |
| 7 L/100km | 33.6 MPG (US) / 40.4 MPG (UK) |
| 5 L/100km | 47.0 MPG (US) / 56.5 MPG (UK) |
| 1 US gallon | 3.785 L |
| 1 UK gallon | 4.546 L |
Frequently asked questions
- Why is improving from 10 MPG to 20 MPG a bigger deal than 40 to 50 MPG?
- MPG is non-linear with consumption. Going from 10 to 20 MPG over 1,000 miles saves 50 gallons of fuel. Going from 40 to 50 MPG over the same distance saves just 5 gallons. L/100km makes this obvious because it's a linear consumption metric — which is part of why most countries use it.
- Are US and UK MPG figures interchangeable?
- No — and this catches lots of people out. A car rated '40 MPG' in a UK magazine is using the Imperial gallon (4.546 L), which is about 20% larger than the US gallon. The same car in the US would be rated about 33 MPG. Always check which gallon a quoted figure is in.
- How do electric vehicles fit into this?
- EVs don't burn gallons, so the US uses 'MPGe' (miles per gallon equivalent) based on the energy in a gallon of gasoline (33.7 kWh). Most other countries use kWh per 100 km or miles per kWh. This converter focuses on liquid-fuel vehicles — for EV efficiency the units are simpler: less energy per distance is better.
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