mpg to l/100 km: fuel consumption converter and trip fuel cost
Convert fuel consumption between litres per 100 km, km per litre and US or UK miles per gallon, and work out the fuel and cost of a trip. Formulas from NIST's gallon and mile.
Fuel consumption
Enter a number, for example 500 or 7.5.
- l/100 km
- 30
- km/l
- 3.33
- mpg (US)
- 7.84
- mpg (UK)
- 9.42
Common values
| l/100 km | km/l | mpg (US) | mpg (UK) |
|---|---|---|---|
| 20 | 5 | 11.76 | 14.12 |
| 25 | 4 | 9.41 | 11.3 |
| 28 | 3.57 | 8.4 | 10.09 |
| 30 | 3.33 | 7.84 | 9.42 |
| 32 | 3.13 | 7.35 | 8.83 |
| 35 | 2.86 | 6.72 | 8.07 |
| 40 | 2.5 | 5.88 | 7.06 |
Fuel for a trip
- Fuel used
- 300 l
- Fuel cost
- 450
- Cost per km
- 0.45
Two directions of measuring
Litres per 100 km says how much fuel a distance takes; the lower the figure, the more economical the truck. Kilometres per litre and miles per gallon say how far a quantity of fuel goes; there the higher figure is the better one. Because one is the reciprocal of the other, the conversion is a division, not a multiplication: halving the l/100 km figure doubles the mpg.
The formulas
- l/100 km = 100 ÷ (km per litre)
- l/100 km = 235.2146 ÷ (US mpg)
- l/100 km = 282.4809 ÷ (UK mpg)
The same three rules work in the other direction: km per litre = 100 ÷ (l/100 km), and so on.
Where the constants come from
A mile is exactly 1.609 344 km, and NIST gives the US gallon as 3.785 412 litres and the imperial gallon as exactly 4.546 09 litres (Special Publication 811, Appendix B.8). 100 × 3.785412 ÷ 1.609344 = 235.2146, and 100 × 4.54609 ÷ 1.609344 = 282.4809 (our arithmetic). NIST’s own table states the US rule as “divide 235.215 by number of miles per gallon”, the same constant rounded to three decimals.
Fuel for a trip
The second calculator multiplies the distance by the consumption: 1,000 km at 30 l/100 km takes 300 litres, and the cost is those litres times the price per litre, in whatever currency the price is entered. It does not know the price of fuel anywhere and uses no exchange rate.
Quick answers
- How do I convert mpg to l/100 km?
- Divide 235.215 by the US mpg figure, which is NIST's rule, or 282.481 by the UK mpg figure: 6.5 US mpg is 36.19 l/100 km, and 8 UK mpg is 35.31 l/100 km.
- What is 30 l/100 km in mpg?
- 7.84 US mpg or 9.42 UK mpg, and 3.33 km per litre.
- Why are US and UK mpg different?
- The gallons differ. NIST gives the US gallon as 3.785412 litres and the imperial gallon used in the UK as exactly 4.54609 litres, so the same consumption gives a UK mpg figure about 20 % higher than the US one.
Sources
- NIST Guide to the SI (Special Publication 811), Appendix B.8: Factors for units listed alphabetically — National Institute of Standards and Technology (NIST)