How the calculation works
In US units, fuel needed is the distance divided by your MPG. In metric, it is the distance multiplied by your L/100km figure, divided by 100. Multiply the fuel needed by the price per gallon or litre and you have the trip cost.
US: cost = (miles ÷ MPG) × price per gallon
Metric: cost = (km × L/100km ÷ 100) × price per litre
Frequently asked questions
Fill the tank, reset the trip meter and drive as usual. At the next fill-up, divide the miles driven by the gallons you added (or litres added × 100 ÷ km driven for L/100km).
Highway speed, stop-and-go traffic, air conditioning, low tire pressure and heavy loads all raise consumption above the rated figure.