What is the MPG Calculator?
The MPG calculator converts distance and fuel used into miles per gallon, and shows the same economy in litres per 100 km and kilometres per litre.
How to use the MPG tool
- Enter Distance driven and Fuel used.
- The result updates instantly as you type, or press Calculate.
- Use Try an example to see how it works, and Reset to start again.
Formula
MPG = miles ÷ US gallons. L/100 km = 235.215 ÷ MPG. km/L = MPG × 0.425144.
Worked example
With distance driven 350 miles, fuel used 12 US gallons, the fuel economy comes to 29.17 mpg. Litres per 100 km: 8.06; Kilometres per litre: 12.4.
Frequently asked questions
What is a good MPG?
Many modern petrol cars achieve 25 to 35 mpg, hybrids often exceed 45 mpg.
US or imperial gallons?
This tool uses US gallons. An imperial gallon is larger, about 1.2 US gallons.
MPG to L/100 km and km/L
US gallons. L/100 km = 235.215 ÷ mpg; km/L = mpg × 0.425144.
| MPG (US) | L/100 km | km/L |
|---|---|---|
| 10 | 23.52 | 4.25 |
| 15 | 15.68 | 6.38 |
| 20 | 11.76 | 8.5 |
| 25 | 9.41 | 10.63 |
| 30 | 7.84 | 12.75 |
| 35 | 6.72 | 14.88 |
| 40 | 5.88 | 17.01 |
| 45 | 5.23 | 19.13 |
| 50 | 4.7 | 21.26 |
| 60 | 3.92 | 25.51 |
FAQ
What is 30 mpg in L/100 km? 7.84 L/100 km.
Are UK and US mpg the same? No. A UK gallon is 4.546 L, a US gallon 3.785 L.
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Checked by Calcovate · Formula tested against worked examples · Updated 7 Nov 2026 · How we check our calculators.