How to Calculate Fuel Cost for a Journey

What you need to know

To estimate the fuel cost of a journey, you need the trip distance, your vehicle’s fuel economy and the current fuel price. A return trip should include the full distance in both directions.

Fuel economy may be shown as miles per gallon (MPG), kilometres per litre or litres per 100 km. Use matching units or convert them before calculating.

Want to try the idea yourself? Use the Fuel Cost & Trip Calculator.

The basic calculation

First estimate how much fuel the journey will use. Then multiply that amount by the price per litre or gallon.

For example, a 200 km trip in a car using 6 litres per 100 km needs about 12 litres. If fuel costs £1.50 per litre, the estimated fuel cost is £18.

Calculating from MPG

With MPG, divide the journey distance in miles by the vehicle’s miles per gallon to estimate gallons used. If your fuel price is quoted per litre, you then need the appropriate gallon-to-litre conversion before multiplying by the price.

Be careful whether the MPG figure uses UK imperial gallons or US gallons, because they are different sizes.

Why real fuel use can differ

Published fuel economy is an estimate. Speed, traffic, hills, weather, tyre pressure, vehicle load and driving style can all change actual consumption. Stop-start city driving may use considerably more fuel than a steady motorway journey.

For budgeting, it can be sensible to allow a little extra rather than treating the calculated amount as exact.

Compare trip costs quickly

The Fuel Cost & Trip Calculator handles the arithmetic and makes it easier to compare journeys, fuel prices or different efficiency figures.

It can also help when splitting a trip cost between passengers: calculate the estimated total first, then divide it by the number of people contributing.