How the cost is worked out
The fuel used is the distance divided by the fuel economy; the cost is the fuel used times the price. With liters per 100 km, multiply the distance by the economy and divide by 100. Mixed units are converted first, using 1 mile = 1.609344 km and 1 US gallon = 3.785412 liters [1].
Fuel used = distance ÷ mpg Cost = fuel used × price
In liters: fuel = km × (L/100 km) ÷ 100. A round trip doubles the distance; the split divides the cost by the people.
Example: miles and mpg
300 miles each way at 28 mpg, fuel at $3.40 a gallon (a made-up price), round trip, split 4 ways.
- Distance: 300 × 2 = 600 miles
- Fuel: 600 ÷ 28 = 21.43 gallons
- Cost: 21.43 × $3.40 = $72.86; $18.21 each
Example: kilometers and L/100 km
480 km at 8.4 L/100 km, fuel at $1.65 a liter (made up).
- Fuel: 480 × 8.4 ÷ 100 = 40.32 liters
- Cost: 40.32 × $1.65 = $66.53
Questions
Where do I get the fuel price?
Enter what you expect to pay: the price on the pump sign or your last receipt. This page does not supply current prices. The price changes by place and by week, so a figure here would go stale.
How do I convert mpg to liters per 100 km?
Divide 235.215 by the mpg. So 28 mpg is 8.4 L/100 km. The same division converts back. The number comes from 100 × 3.785412 liters per US gallon ÷ 1.609344 km per mile [1].
Is this the US gallon?
Yes, miles per US gallon and a price per US gallon. A US gallon is 3.785412 liters [1]. An imperial gallon is larger, so UK mpg figures are not interchangeable with these.
Will I really get my rated mpg?
Not necessarily. Speed, load, weather and traffic change it. Use the mpg you see on your own trips for the closest estimate.
What does the round trip option do?
It doubles the distance you enter before working out the fuel, so enter one way and tick the box for a return journey.