How this number is made
Fuel cost is the volume the trip uses times the price on the sign. In miles, volume is distance divided by miles per gallon. In kilometers, volume is distance divided by 100, times liters per 100 km. Use the figure you actually get, not the brochure.
- Choose miles or kilometers. Use the round-trip distance if you are coming back. The form does not double it.
- In miles, read mpg from a recent tank: miles driven ÷ gallons filled. In kilometers, use liters per 100 km from the same tank.
- Split only the fuel. Tolls and the driver’s time are a separate conversation.
Formula
Gallons = miles ÷ mpg. Liters = kilometers ÷ 100 × liters per 100 km. Cost = volume × price. Each person = cost ÷ people.
Worked example
360 miles at 28 mpg is about 12.9 gallons. At $3.40 a gallon the drive is about $43.71, or $21.86 if two people share fuel. In metric, 580 km at 7.2 L/100 km is 41.76 liters. At 1.65 per liter the same kind of trip is about 68.90.
Questions
What about electric cars?
Use the electricity calculator. Miles per gallon does not describe a kilowatt-hour. A rough mpg-equivalent will not match your utility rate.
Does speed matter?
Yes, and this page ignores it. Above highway speeds, mpg usually falls. If the drive is fast, lower the mpg rather than trusting the brochure.