Fuel Cost Calculator
Estimate the fuel cost of a trip from the distance, your vehicle's fuel economy, and the price of fuel — with round-trip and per-person totals.
Comment utiliser cette calculatrice
- 1Enter the trip distance in miles or kilometres.
- 2Enter your vehicle's fuel economy and select its unit — mpg, L/100 km, or km/L.
- 3Enter the fuel price and choose whether it is priced per gallon or per litre.
- 4Optionally split the cost between passengers for a carpool.
Comment ça marche
Fuel cost of a trip
fuel used = distance ÷ fuel economy cost = fuel used × fuel price combined: cost = distance × fuel price ÷ fuel economy watch the units — US and UK gallons differ by ~20%
The calculation is a single division and multiplication, but units are where it goes wrong. A US gallon (3.785 L) is about 20% smaller than a UK gallon (4.546 L), so a '30 mpg' rating means noticeably different things in each country. This calculator normalises everything to kilometres and litres internally, so you can mix a US-gallon fuel price with a mpg rating or a litres-per-100 km figure without doing the conversion yourself.
Exemple détaillé
A 300-mile trip in a car doing 30 mpg (US) with fuel at $3.50 per US gallon: 300 ÷ 30 = 10 gallons, times $3.50 = $35 one way, or $70 for the round trip.
Fuel Cost Calculator : le guide complet
Mind the gallon
The single biggest source of error in fuel-cost estimates is the gallon. A US gallon is 3.785 litres; a UK (imperial) gallon is 4.546 litres — nearly 21% larger. A car rated at 40 mpg in the UK is only about 33 mpg by the US measure, because a UK gallon simply holds more fuel. Quoting a UK economy figure against a US fuel price, or vice versa, produces a badly wrong answer.
Much of the world sidesteps the problem entirely by measuring fuel use as litres per 100 kilometres, where a lower number is better and there is no gallon to confuse. This calculator accepts all of these — mpg (US and UK), litres per 100 km, and kilometres per litre — and reconciles them internally, so you can use whichever numbers are printed on your car and at your pump.
Fuel is only part of the cost of driving
Fuel is the most visible cost of a trip, but it is rarely the largest cost of owning a car. Depreciation — the value the car loses simply by ageing and accumulating miles — usually exceeds fuel over the life of a vehicle. Add insurance, maintenance, tyres, and repairs, and the true cost per mile is often two to three times the fuel cost alone.
For a fair comparison between driving and other options, or between two vehicles, the fuel figure here is the starting point rather than the whole picture. Tax authorities publish a standard mileage rate precisely to capture this fuller cost; in the United States it is well above the fuel-only figure this calculator produces.
Why your real economy is worse than the sticker
Official fuel-economy ratings come from standardised laboratory tests, and real-world driving almost always does worse. Cold starts, short trips, air conditioning, roof racks, aggressive acceleration, high speeds, and hills all cut efficiency, sometimes by 20% or more. Highway cruising at a steady 60 mph is close to the best a car achieves; stop-and-go city traffic is far from it.
For a realistic budget, use your own measured economy rather than the sticker. Fill the tank, note the odometer, drive normally, fill again, and divide the miles driven by the fuel added. A few tanks of this gives a number that reflects how and where you actually drive, which is what the estimate above depends on.
Questions fréquentes
How do I calculate the fuel cost of a trip?
Divide the distance by your fuel economy to get the fuel used, then multiply by the fuel price: cost = distance × price ÷ economy. The only trap is units — make sure your economy and price use the same size of gallon, or convert to litres, which this calculator does automatically.
What is the difference between US and UK mpg?
The gallon. A UK gallon is about 20% larger than a US gallon, so a UK mpg figure looks better for the same real efficiency. 40 UK mpg equals roughly 33 US mpg. Always match your economy figure to the gallon your fuel price uses.
Does this include wear, insurance, and depreciation?
No — it estimates fuel only. The full cost of driving also includes depreciation (often the biggest expense), insurance, maintenance, and tyres, which together typically exceed the fuel cost. Use a standard mileage rate if you need the complete per-mile figure.
Why is my real fuel economy lower than the rating?
Official ratings come from lab tests under ideal conditions. Cold weather, short trips, high speeds, air conditioning, and hard acceleration all reduce efficiency in real driving, commonly by 10–20%. Measure your own economy over a few tanks for an accurate trip budget.