Fuel Economy Converter 2026: MPG (US/UK) to L/100 km
30 US mpg is 7.84 L/100 km and 30 UK mpg is 9.42. Switch between mpg, L/100 km and km/L, then work out the litres, gallons and fuel cost of a road trip.
Convert fuel economy: type in any box
US and UK (Imperial) miles per gallon differ because the gallons differ: 1 US gallon = 3.785411784 L, 1 Imperial gallon = 4.54609 L, 1 mile = 1.609344 km.
30 mpg (US) is 36.03 mpg (UK), 7.84 L/100 km or 12.75 km/L.
Higher mpg and km/L mean less fuel used; higher L/100 km means more.
Trip fuel and cost estimate
Enter the distance, your car’s economy in any unit and the pump price. The price can be in any currency; the result is in the same currency.
An estimate from the figures you enter. Real consumption changes with speed, load, weather and terrain.
mpg to L/100 km chart
Common US mpg figures and their equivalents.
| mpg (US) | mpg (UK) | L/100 km | km/L |
|---|---|---|---|
| 15 | 18.0 | 15.68 | 6.38 |
| 20 | 24.0 | 11.76 | 8.50 |
| 25 | 30.0 | 9.41 | 10.63 |
| 30 | 36.0 | 7.84 | 12.75 |
| 35 | 42.0 | 6.72 | 14.88 |
| 40 | 48.0 | 5.88 | 17.01 |
| 45 | 54.0 | 5.23 | 19.13 |
| 50 | 60.0 | 4.70 | 21.26 |
| 55 | 66.1 | 4.28 | 23.38 |
| 60 | 72.1 | 3.92 | 25.51 |
L/100 km to mpg chart
The figures European and Australian brochures quote, in US and UK mpg.
| L/100 km | mpg (US) | mpg (UK) | km/L |
|---|---|---|---|
| 3 | 78.4 | 94.2 | 33.33 |
| 4 | 58.8 | 70.6 | 25.00 |
| 5 | 47.0 | 56.5 | 20.00 |
| 6 | 39.2 | 47.1 | 16.67 |
| 7 | 33.6 | 40.4 | 14.29 |
| 8 | 29.4 | 35.3 | 12.50 |
| 9 | 26.1 | 31.4 | 11.11 |
| 10 | 23.5 | 28.2 | 10.00 |
| 11 | 21.4 | 25.7 | 9.09 |
| 12 | 19.6 | 23.5 | 8.33 |
30 miles per US gallon is 7.84 litres per 100 km, and 30 miles per UK gallon is 9.42. The gap is not a rounding error: the American and Imperial gallons are different sizes, so a brochure figure from Britain and one from the US cannot be compared until both are in the same unit. Type any figure above and the converter gives all four common units at once.
The conversion factors
- 1 US gallon = 3.785411784 litres; 1 Imperial (UK) gallon = 4.54609 litres; 1 mile = 1.609344 km.
- US mpg to L/100 km: 235.215 ÷ mpg. 25 US mpg is 9.41 L/100 km.
- UK mpg to L/100 km: 282.481 ÷ mpg. 50 UK mpg is 5.65 L/100 km.
- US mpg to UK mpg: multiply by 1.20095. km/L is 100 ÷ L/100 km.
Because L/100 km is fuel per distance and mpg is distance per fuel, one goes down as the other goes up. That is why the charts are not straight lines: improving from 20 to 25 US mpg saves more fuel (2.35 L/100 km) than improving from 45 to 50 (0.52 L/100 km).
Estimating a road trip
The trip box multiplies distance by consumption and price. Enter the price per litre, per US gallon or per UK gallon in whatever currency you pay; the cost comes out in the same currency. For country-by-country pump prices and tolls, use the fuel cost calculator or the road trip cost calculator.
Tyres (tires) and fuel economy
Tyre size and pressure can both affect consumption. A different size alters the rolling circumference, which also shifts the trip computer’s distance reading, so compare sizes in the tyre size calculator first. Running the pressure the vehicle maker specifies matters as well: convert the placard figure with the tyre pressure converter or get a size-based estimate from the tyre pressure calculator, and see the tyre pressure guide for how to check it.
Frequently Asked Questions
30 US mpg is 7.84 L/100 km. 30 UK (Imperial) mpg is 9.42 L/100 km. The UK figure converts to more litres because the Imperial gallon is bigger, so check which gallon a figure uses before converting.
The gallons differ. A US gallon is 3.785411784 litres and an Imperial (UK) gallon is 4.54609 litres, so a UK mpg figure is about 20.1% higher than the US figure for the same consumption. 40 US mpg is 48.0 UK mpg.
Divide 235.215 by the L/100 km figure for US mpg, or divide 282.481 by it for UK mpg. So 6 L/100 km is 39.2 US mpg or 47.1 UK mpg, and 5 L/100 km is 47.0 US mpg or 56.5 UK mpg.
No. L/100 km measures fuel used per distance, so lower is better. mpg and km/L measure distance per unit of fuel, so higher is better. A car going from 6 to 5 L/100 km uses one sixth less fuel.