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How to Calculate Fuel Cost for a Trip

By Dr. Ahmed Mortuza Saleque · Updated · How we check our content

The short answer

Trip fuel cost = distance ÷ fuel economy × fuel price. Driving 300 miles in a car that gets 30 mpg uses 10 gallons; at $3.50 a gallon that costs $35. In metric, 500 km at 7 L/100 km uses 35 litres, which costs €63 at €1.80 a litre.

Open the Fuel Cost Calculator →

The formula, step by step

  1. Find the trip distance from a maps app. For a return journey, double it.
  2. Divide by your car's fuel economy to get the fuel needed: 300 miles ÷ 30 mpg = 10 gallons.
  3. Multiply by the fuel price: 10 × $3.50 = $35.

In metric units, fuel needed = distance ÷ 100 × litres per 100 km: 500 ÷ 100 × 7 = 35 litres. The fuel cost calculator handles both systems.

Fuel cost per 100 miles

Cost to drive 100 miles at different fuel prices.

Fuel economy$3.00 a gallon$3.50 a gallon$4.00 a gallon
20 mpg$15.00$17.50$20.00
25 mpg$12.00$14.00$16.00
30 mpg$10.00$11.67$13.33
35 mpg$8.57$10.00$11.43
40 mpg$7.50$8.75$10.00
50 mpg$6.00$7.00$8.00

Multiply the figure by your distance in hundreds of miles. A 450-mile trip at 30 mpg and $3.50 a gallon costs 4.5 × $11.67 = $52.50.

Cost per mile

Divide the fuel price by your mpg: $3.50 ÷ 30 = about 11.7 cents a mile. Over 12,000 miles a year that is $1,400 in fuel. An electric car using 0.3 kWh per mile at $0.16 per kWh costs about 4.8 cents a mile; the electricity cost guide explains that calculation.

Fuel is only part of the cost of driving. Tyres, servicing, insurance and depreciation usually add more per mile than fuel does.

Finding your real fuel economy

Official figures are measured in laboratory tests, and real driving is usually less efficient. To measure yours, fill the tank and reset the trip meter; at the next fill-up, divide the miles driven by the gallons added. 320 miles on 11.2 gallons is 28.6 mpg.

Motorway speeds above about 65 mph, roof boxes, heavy loads, cold weather and short trips all lower fuel economy. To convert between units, 235.2 ÷ mpg (US) gives L/100 km: 30 mpg is 7.8 L/100 km. The fuel economy converter covers UK gallons and km per litre too.

Splitting the cost

Divide the total by the number of people in the car, driver included. A 600-mile return trip at 30 mpg and $3.50 a gallon costs $70, which is $17.50 each for four people. Add tolls and parking before dividing.

Common questions

How much fuel will I use on a trip?

Divide the distance by your fuel economy. 300 miles at 30 mpg uses 10 gallons. In metric, 500 km at 7 L/100 km uses 35 litres.

How do I calculate fuel cost per mile?

Divide the price per gallon by your miles per gallon. $3.50 ÷ 30 mpg is about 11.7 cents a mile.

How much does it cost to drive 1,000 miles?

At 30 mpg and $3.50 a gallon, 1,000 miles uses 33.3 gallons and costs about $116.67. At 25 mpg it costs $140.

How do I convert mpg to litres per 100 km?

Divide 235.2 by the US mpg figure. 40 mpg is 5.9 L/100 km.

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