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.
Australia is fully metric under the National Measurement Act 1960; imperial units appear only in trade with the US and in older documents.
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 Measurement Institute (NMI) — Australia's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.