Quick answer: 600 km on 45 litres is 600 ÷ 45 = 13.33 km/L, or 45 ÷ 600 × 100 = 7.5 L/100 km, which is 31.36 US mpg.
How it's calculated
km per litre = distance ÷ fuel. Litres per 100 km = fuel ÷ distance × 100. The first is distance per fuel (higher is better), the second fuel per distance (lower is better), and each is 100 divided by the other.
Miles per gallon depends on the gallon: a US gallon is 3.785411784 L and a UK (imperial) gallon is 4.54609 L, with 1 mile = 1.609344 km. That gives US mpg = 235.215 ÷ L/100 km and UK mpg = 282.481 ÷ L/100 km.
For a fair figure, fill the tank to full, reset the trip meter, drive as usual, then fill up again and enter the distance and the litres you added.
Worked examples
- 600 km, 45 L: 13.33 km/L, 7.5 L/100 km, 31.36 US mpg, 37.66 UK mpg
- 373 miles, 12 US gallons: 31.08 mpg = 7.57 L/100 km = 13.21 km/L
Frequently asked questions
Why do US and UK mpg differ?
The gallons differ: the UK gallon is about 20% bigger, so the same car shows a higher mpg in UK units.
What is good fuel economy?
There's no single number. Compare yours with the official rating for your model and with your own earlier fill-ups; a sudden drop is worth a look.
How do I turn this into a trip cost?
Use the fuel cost calculator with your L/100 km or km/L and the current price per litre.
How do I convert km/L to mpg?
Multiply by 2.352 for US mpg or 2.825 for UK mpg. 12.5 km/L works out to about 29.4 US mpg, or 35.3 UK mpg.
Why is my real consumption higher than the official figure?
Official figures come from lab tests in mild conditions. Real driving adds heat, the AC, short trips, traffic, motorway speeds and luggage, and all of them push consumption up.
How many fill-ups should I measure?
One full-to-full fill-up is a fair start. Average three or more and the result smooths out differences in how full the pump fills the tank and in your driving week to week.