Why this is useful
For road trips, fuel is often the biggest variable cost and the easiest one to split fairly between passengers.
How it is calculated
Fuel needed = distance × journeys × consumption ÷ 100. Cost = fuel needed × price per litre, then divided by the number of people sharing.
Worked example
Example only: a 450 km return trip in a car using 7 L/100 km needs 63 litres. At a hypothetical 1.80 per litre that is about 113, or 57 each for two people.
Common mistakes
- Using the manufacturer's best-case consumption — real driving, hills and air-conditioning use more.
- Mixing units: US mpg, UK mpg and L/100 km are different measures.
- Forgetting tolls, parking and ferry crossings, which are not fuel.
Questions
How do I convert mpg to L/100 km?
For US gallons, divide 235.2 by the mpg figure. For UK (imperial) gallons, divide 282.5 by the mpg figure.
Where do I find the fuel price?
Use a current local price from a fuel station or official pricing site for the country you will drive in; prices change frequently.