Fuel Economy Converter
Convert liters per 100 km to mpg — and between UK and US mpg, which use different gallons — plus kilometers per liter. Results update as you type; exact factors shown.
One miles per US gallon is 235.2146 liters per 100 km — see the exact factor, not a rounded rule of thumb.
How the fuel economy 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 US uses customary units (US gallon, short ton, °F) in daily life; NIST SP 811 gives the exact SI factors.
Common fuel economy conversions
| From | To | Units |
|---|---|---|
| 7 L/100 km | 33.6021 mpg (US) | liters per 100 km to miles per US gallon |
| 7 L/100 km | 40.3544 mpg (UK) | liters per 100 km to miles per imperial gallon |
| 30 mpg (US) | 7.8405 L/100 km | miles per US gallon to liters per 100 km |
| 40 mpg (UK) | 7.062 L/100 km | miles per imperial gallon to liters per 100 km |
| 5 L/100 km | 20 km/L | liters per 100 km to kilometers per liter |
| 15 km/L | 6.6667 L/100 km | kilometers per liter to liters per 100 km |
| 10 L/100 km | 23.5215 mpg (US) | liters per 100 km to miles per US gallon |
| 50 mpg (UK) | 41.6337 mpg (US) | miles per imperial gallon to miles per US gallon |
| 25 mpg (US) | 30.0237 mpg (UK) | miles per US gallon to miles per imperial gallon |
| 4.5 L/100 km | 62.7735 mpg (UK) | liters per 100 km to miles per imperial gallon |
Units in this converter and their exact factors
| Unit | Symbol | To L/100 km |
|---|---|---|
| liters per 100 km | L/100 km | x |
| kilometers per liter | 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
Why is UK mpg higher than US mpg for the same car?
An imperial gallon is 4.546 L, a US gallon 3.785 L — 20% more fuel per gallon, so 20% more miles per gallon.
What is 7 L/100 km in mpg?
33.6 mpg (US) or 40.4 mpg (UK).
How do I convert mpg to L/100 km?
Divide 235.215 by US mpg, or 282.481 by UK mpg.
Is a lower L/100 km better?
Yes — it is fuel used per distance, so lower means more economical. With mpg, higher is better.
What is good fuel economy?
Roughly under 6 L/100 km (over 39 mpg US / 47 mpg UK) for a petrol car; hybrids reach 4 L/100 km; EVs are rated in kWh/100 km instead.
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 Institute of Standards and Technology (NIST) — United States's national measurement authority.
Last checked: September 2026. Conversion factors are fixed by definition and do not change with tax years or regulations.