How trip fuel cost is calculated
The calculator converts everything to a common basis. In metric mode, litres used equal distance times consumption divided by 100. In miles mode, gallons used equal miles divided by mpg. Cost is the fuel used times the price per litre or gallon.
Because countries use different units, the tool offers three setups: kilometres with L/100 km, US miles with mpg and a price per gallon, and UK miles with mpg and a price per litre.
A worked example
In metric: a 300 km trip at 7 L/100 km uses 21 litres. At 1.80 a litre the cost is 37.80, or about 0.126 per km.
In the US: a 200 mile trip at 30 mpg uses 6.67 gallons. At 3.50 a gallon that costs 23.33, around 0.117 per mile. Sharing between four people brings it to about 5.83 each.
Ways to spend less on fuel
Steady driving, correct tyre pressure and removing roof boxes can all reduce consumption. Combining trips and sharing rides help too. Even a small change in L/100 km adds up over a year.
When comparing cars, use the same unit for each and look at the cost per distance rather than the headline price.
Notes
Prices and consumption change, so this is a planning estimate. Fuel economy figures quoted in brochures are usually from lab tests and tend to be better than real-world use.
Questions people ask
How do I calculate the fuel cost of a trip?
Work out how much fuel the trip uses, then multiply by the price. At 7 L/100 km, a 300 km trip uses 21 litres. At 1.80 per litre that costs 37.80.
What is the difference between US and UK mpg?
A US gallon is 3.785 litres and a UK (imperial) gallon is 4.546 litres, so the same car shows a higher mpg figure in the UK. 30 mpg in the US is about 36 mpg in UK terms. Pick the setting that matches how your car reports consumption.
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure to get litres per 100 km. 30 US mpg is about 7.8 L/100 km. For UK mpg, divide 282.481 by the figure instead.
Why is my real fuel use different?
Speed, traffic, hills, load, air conditioning, tyre pressure and temperature all change consumption. Use the average figure from your trip computer, or work it out from your last few tanks.
Does it include tolls or parking?
No, only fuel. Add tolls, parking and any wear costs separately if you need the full cost of a journey.