How to use
- Type a fuel economy figure in Value, such as 30 mpg.
- Pick the From and To units. US and UK mpg are listed separately.
- Read the answer. The formula for your pair is shown under it.
Formula
mpg and km/L measure distance per unit of fuel, so higher is better. L/100 km and gallons per 100 miles measure fuel per distance, so lower is better. Converting between the two kinds means dividing, not multiplying:
L/100 km = 235.215 ÷ US mpg
L/100 km = 282.481 ÷ UK mpg
km/L = US mpg × 0.425144
UK mpg = US mpg × 1.200950
The UK (imperial) gallon is about 20% bigger than the US gallon, so the same car scores about 20% higher in UK mpg.
Examples
- 30 US mpg to L/100 km: 235.215 ÷ 30 = 7.84 L/100 km
- 6 L/100 km to mpg: 39.2 US mpg, or 47.08 UK mpg
- 15 km/L to mpg: 15 ÷ 0.425144 = 35.28 US mpg
- 25 mpg on a US label: 100 ÷ 25 = 4 gallons per 100 miles
Conversion charts
| US mpg | L/100 km | km/L | UK mpg |
|---|---|---|---|
| 15 | 15.68 | 6.38 | 18 |
| 20 | 11.76 | 8.5 | 24 |
| 25 | 9.41 | 10.63 | 30 |
| 30 | 7.84 | 12.75 | 36 |
| 35 | 6.72 | 14.88 | 42 |
| 40 | 5.88 | 17.01 | 48 |
| 50 | 4.7 | 21.26 | 60 |
| L/100 km | US mpg | UK mpg | km/L |
|---|---|---|---|
| 4 | 58.8 | 70.6 | 25 |
| 5 | 47 | 56.5 | 20 |
| 6 | 39.2 | 47.1 | 16.67 |
| 7 | 33.6 | 40.4 | 14.29 |
| 8 | 29.4 | 35.3 | 12.5 |
| 10 | 23.5 | 28.2 | 10 |
| 12 | 19.6 | 23.5 | 8.33 |
More detail: the mpg illusion
- Fuel used depends on 1 ÷ mpg, so gains at the low end matter most.
- Over 1,000 miles, going from 10 to 15 mpg saves about 33.3 gallons. Going from 30 to 35 mpg saves only about 4.8 gallons.
- That’s why US labels also show gallons per 100 miles, and Europe uses L/100 km.
- Zero and negative values can’t be converted, because 0 mpg would mean infinite fuel per distance.
Working out a trip’s fuel volume? Use the volume converter.