The simple formula
Fuel cost = (distance ÷ efficiency) × price per unit. Divide the trip distance by your miles-per-gallon (or km per litre) to get fuel used, then multiply by the price. A 300-mile trip in a 30-MPG car at $3.50/gallon uses 10 gallons and costs $35. Keep your units consistent — miles with MPG and price per gallon, or kilometres with your local equivalents.
Cost per mile: the number that compares cars
Dividing price by efficiency gives cost per mile — a clean way to compare vehicles or plan budgets. At $3.50/gallon, a 30-MPG car costs about 12¢/mile in fuel; a 20-MPG SUV costs 17.5¢; a 45-MPG hybrid just 7.8¢. Over 12,000 miles a year, that spread is hundreds of dollars — and it compounds over the years you own the vehicle.
Beyond the pump price
- Fuel is only part of driving cost. Insurance, maintenance, tyres, and depreciation often exceed fuel — factor them in when comparing cars or commutes.
- Efficiency varies with conditions. Highway driving, gentle acceleration, and proper tyre pressure improve real-world MPG; city stop-and-go and heavy loads worsen it.
- Commute math: a longer commute to a cheaper home has a real, recurring fuel (and time) cost worth putting a number on before you decide.
For electric vehicles the same logic applies with cost per kWh and miles per kWh — the per-mile figure is usually much lower, which is a core part of the EV value case alongside their higher purchase price.