Fuel Cost Calculator
Enter the trip distance, your car’s fuel economy and the price of fuel. The calculator works out how much fuel the trip uses, what it costs and the cost per mile or kilometre, in miles per gallon or litres per 100 km.
Answer
Fuel cost
35.00
10 gallons of fuel for 300 mi.
- gallons used
- 10
- cost per mile
- 0.117
- each, if split between two
- 17.50
Check the work
Every line comes from the same calculation as the answer.
cost = fuel used × price
| fuel | 300 ÷ 30 | 10 gal |
|---|---|---|
| cost | 10 × 3.5 | 35.00 |
| per mile | 35 ÷ 300 | 0.1167 |
How it works
Fuel cost is fuel used times fuel price, and fuel used comes from distance and economy. The only trap is that economy is quoted two opposite ways. Miles per gallon says how far one gallon goes, so you divide the distance by it. Litres per 100 km says how much fuel a fixed distance takes, so you multiply.
A 300-mile trip in a car that does 30 mpg uses 10 gallons; at 3.50 a gallon that is 35.00. A 500 km trip at 6.5 L/100 km uses 32.5 litres; at 1.80 a litre that is 58.50. The price is in whatever currency you pay in.
Economy on a real trip differs from the figure on the window sticker. Motorway speeds, a loaded car, roof boxes, cold weather and stop-start traffic all change it. Using the economy you actually get from your trip computer or fill-up records gives a much better estimate.
Formula
mpg: fuel = distance ÷ mpg · L/100 km: fuel = distance × L ÷ 100; cost = fuel × price
Fuel used is found from the distance and the economy, in the direction each unit requires, and multiplied by the price per gallon or litre.
Worked examples
- Try these numbers
300 miles at 30 mpg, fuel at 3.50 a gallon
- 300 ÷ 30 = 10 gallons.
- 10 × 3.50 = 35.00.
- 35.00 ÷ 300 = 0.117 per mile.
The trip costs 35.00 in fuel.
- Try these numbers
500 km at 6.5 L/100 km, fuel at 1.80 a litre
- 500 × 6.5 ÷ 100 = 32.5 litres.
- 32.5 × 1.80 = 58.50.
- 58.50 ÷ 500 = 0.117 per km.
The trip costs 58.50 in fuel.
- Try these numbers
Fuel used when the price is not known yet
- 100 ÷ 25 = 4 gallons.
- With a price of 0 the cost shows as 0; the fuel figure is still correct.
The trip uses 4 gallons.
Inputs and results
- Distance
- Trip distance in miles or kilometres.
- Fuel economy
- US miles per gallon, or litres per 100 km.
- Fuel price
- Price per US gallon or per litre, in your currency.
- Fuel used
- Gallons or litres the trip needs.
- Fuel cost
- Fuel used times fuel price.
- Cost per mile or km
- Fuel cost divided by distance.
When to use it
- Budgeting for a road trip or a holiday drive.
- Splitting fuel costs fairly between people sharing a car.
- Comparing the fuel cost of driving with the price of a train or bus ticket.
Common mistakes
- Mixing imperial and US gallons: this calculator uses the US gallon of 3.785 litres for mpg.
- Entering a return trip as one-way distance; double the distance for a round trip.
- Treating litres per 100 km like mpg. A lower L/100 km figure means better economy, the opposite of mpg.
What it does not do
- It does not fetch live fuel prices; enter the price you expect to pay.
- It uses one economy figure for the whole trip and does not model hills, speed or traffic.
- It covers fuel only, not tolls, parking, wear or the cost of owning the car.
Method and assumptions
In miles per gallon, fuel is the distance divided by the economy. In litres per 100 km, fuel is the distance multiplied by the economy and divided by 100.
Cost is fuel times the price per unit of fuel, and cost per distance is the cost divided by the distance. No rounding is applied before the final display.
Assumptions
- Economy is constant over the whole trip.
- Gallons are US gallons.
- The price is per gallon or per litre to match the economy unit.
Edge cases
- A fuel price of 0 is allowed and gives a cost of 0.
- A distance or economy of 0 is refused, because no trip or no fuel use cannot be calculated.
- Very high economy figures, such as plug-in hybrids on short trips, are calculated as entered.
Sources and corrections
This calculator uses an elementary formula, so it needs no outside data source. The method, the rounding rules and how a reported error is corrected are set out in the site standards.
Result looks wrong?
Send the inputs you used and the answer you expected. Every report is checked against the formula and its tests, and confirmed errors are corrected in public.