How to work out the fuel cost of a trip
- Enter the one-way Distance in miles or kilometres.
- Enter your car's Fuel economy and pick its unit: US or UK mpg, L/100 km or km/L. Then the Fuel price, per US gallon, UK gallon or litre. Each unit is separate, so miles, UK mpg and a price per litre works.
- Add the number of People sharing if you're splitting the cost.
- Read the trip cost, the fuel used, the cost per mile or km, the round trip cost and each person's share.
A worked example both ways
A 300 mile drive in a car that does 30 mpg, with gas at $3.40 a gallon:
- Fuel used: 300 ÷ 30 = 10 gallons
- Trip cost: 10 × 3.40 = $34.00
- Round trip: $68.00, or $17.00 each if four people share both ways
In metric, a 300 km drive in a car that uses 7 L/100 km, with petrol at 1.75 a litre, uses 300 × 7 ÷ 100 = 21 litres and costs 36.75. The cost per kilometre works out at about 0.12. Note that a lower L/100 km figure means a more economical car, the opposite of mpg, where higher is better.
If you need to switch between the two systems, the mpg to L/100 km converter does it in one step.
Why the real cost can differ
The result is only as good as the fuel economy you enter. Official ratings come from standard test cycles, and your own figure depends on how you drive. Motorway speeds, a roof box, a full load, heavy air conditioning and lots of short trips in a cold engine all use more fuel, while steady cruising at moderate speed uses less.
For a long trip it’s worth allowing for detours, traffic and parking. Tolls, parking fees and wear on the car are not part of the fuel cost, so add those separately if you’re splitting the whole cost of a journey. Fuel prices also vary between stations and regions, so use the price where you expect to fill up.