How to calculate fuel cost for a road trip

Divide the distance by your vehicle's efficiency to find the fuel needed, then multiply by the fuel price. A 500 km trip at 12.5 km per litre needs 40 litres; at 1.50 per litre that costs 60.

Use the same units throughout: kilometres with litres, or miles with gallons.

In some countries efficiency is quoted as litres per 100 km, where lower is better. Divide 100 by the figure to get kilometres per litre: 8 L/100 km is 12.5 km per litre.

To convert US miles per gallon to litres per 100 km, divide 235.215 by the mpg figure. 30 mpg is about 7.84 L/100 km.

Speed, load, traffic, hills, tyre pressure and air conditioning all change consumption. Motorway driving at high speed uses noticeably more fuel than steady driving at moderate speed.

Add a margin of 10% to your estimate for a safer budget, and include tolls and parking separately.

Divide the total fuel cost by the number of people travelling, and agree beforehand whether to include tolls and wear and tear. The trip cost for 4 people from the example is 15 each.

Our fuel cost calculator gives both the fuel used and the cost in one step.