Fuel-cost formula and unit conversions
For a trip using litres per 100 kilometres (L/100 km), estimated fuel used is distance in km × efficiency ÷ 100. Multiply the litres used by the price per litre to estimate trip cost. For miles per gallon (MPG), divide trip miles by MPG to estimate gallons used, then multiply by the price per gallon.
Example
A 300 km trip in a vehicle rated at 8 L/100 km uses about 24 litres. At $1.60 per litre, the estimated fuel cost is $38.40. With MPG, make sure the fuel price is per gallon; with L/100 km, use a price per litre.
The result is an estimate based on the efficiency value you enter. Actual consumption changes with traffic, speed, terrain, weather, vehicle load, tire pressure, and driving style. It excludes tolls, parking, maintenance, and other trip costs.
Tips for accurate results
Use the fuel economy you actually get, which you can work out from your own fill-ups: distance driven divided by fuel added. Include the return trip for round trips and use the price you expect to pay along the route. Highway and city driving can differ noticeably.
Common mistakes and limits
Fuel economy is shown in different ways. Miles per gallon and liters per 100 kilometers are inverses, so a higher mpg is better but a higher L/100 km is worse, and a US gallon is smaller than an imperial gallon. Tolls, parking, maintenance, and wear are not part of this figure.
Learn more: Unit conversion: common mistakes and how to avoid them.