MPG to L/100km Converter
Convert miles per gallon to litres per 100 km — and note these run in opposite directions, so a higher mpg means a lower L/100km. Results update as you type; exact factors shown.
One miles per imperial gallon is 282.4809 litres per 100 km — see the exact factor, not a rounded rule of thumb.
How the mpg to l/100km converter works
Fuel economy is an inverse quantity: lower L/100 km is better, higher mpg is better. mpg (US) = 235.215 / (L/100 km) because a US gallon is 3.785 L and a mile 1.609 km; mpg (UK) = 282.481 / (L/100 km) with the 4.546 L imperial gallon. UK mpg figures are therefore always 20% higher than US mpg for the same car.
The UK is metric for most trade and science but keeps miles, pints, stone and mpg (with the imperial gallon) in daily life.
Common fuel economy conversions
| From | To | Units |
|---|---|---|
| 20 mpg (UK) | 14.124 L/100 km | miles per imperial gallon to litres per 100 km |
| 25 mpg (UK) | 11.2992 L/100 km | miles per imperial gallon to litres per 100 km |
| 30 mpg (UK) | 9.416 L/100 km | miles per imperial gallon to litres per 100 km |
| 35 mpg (UK) | 8.0709 L/100 km | miles per imperial gallon to litres per 100 km |
| 40 mpg (UK) | 7.062 L/100 km | miles per imperial gallon to litres per 100 km |
| 45 mpg (UK) | 6.2774 L/100 km | miles per imperial gallon to litres per 100 km |
| 50 mpg (UK) | 5.6496 L/100 km | miles per imperial gallon to litres per 100 km |
| 55 mpg (UK) | 5.136 L/100 km | miles per imperial gallon to litres per 100 km |
| 60 mpg (UK) | 4.708 L/100 km | miles per imperial gallon to litres per 100 km |
| 70 mpg (UK) | 4.0354 L/100 km | miles per imperial gallon to litres per 100 km |
| 80 mpg (UK) | 3.531 L/100 km | miles per imperial gallon to litres per 100 km |
| 100 mpg (UK) | 2.8248 L/100 km | miles per imperial gallon to litres per 100 km |
Units in this converter and their exact factors
| Unit | Symbol | To L/100 km |
|---|---|---|
| litres per 100 km | L/100 km | x |
| kilometres per litre | km/L | 100÷x |
| miles per imperial gallon | mpg (UK) | 282.480936÷x |
| miles per US gallon | mpg (US) | 235.214583÷x |
FAQFrequently asked questions about fuel economy conversion
Which gallon is this?
The imperial gallon used in the UK. US mpg figures are about 17% lower for the same car.
Why do the two scales run opposite ways?
Because mpg measures distance per fuel and L/100km measures fuel per distance — one is the reciprocal of the other.
What is 40 mpg in L/100km?
About 7.1 L/100km.
Which is the better measure?
L/100km, arguably, because fuel saved scales linearly with it — going from 15 to 14 saves far more than 8 to 7.
What is a good figure?
Under 6 L/100km (about 47 mpg imperial) is efficient for a petrol car.
Where these figures come from
- BIPM — The International System of Units (SI Brochure, 9th edition) — definitions of the base and derived units.
- NIST Special Publication 811 — Guide for the Use of the International System of Units — the exact conversion factors used here.
- National Physical Laboratory (NPL) — United Kingdom's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.