Fuel Cost Calculator
Enter the distance, what the vehicle returns and what you are paying at the pump. You get the fuel for the journey, the fuel it burns, and what each mile is costing you.
Fuel cost
$31.88
- Fuel used
- 9.38 gallons
- Cost per mile
- $0.11
- There and back
- $63.75
- Fuel there and back
- 18.75 gallons
- Fuel only. Tyres, servicing and depreciation are bought by the mile too, and together they usually cost more than the fuel does.
- Real economy is worse than the quoted figure on a cold, short or fully loaded journey, and better than it on a steady motorway run.
About fuel cost
Three numbers decide what a journey costs in fuel: how far it is, how much fuel the vehicle uses to cover that distance, and what the fuel costs. Everything else is arithmetic.
The price is a field here rather than a figure on the page. Fuel moves week to week and differs by a wide margin between a motorway services and a supermarket ten miles away, so any published price would be wrong for most people reading it.
The economy figure is worth being honest about. The number on the brochure is measured under test conditions, and a real journey rarely matches them. A cold engine on a short trip, a full car, a roof box, town traffic and speeds above about 60 all cost more than the quoted figure suggests. A steady motorway run at a moderate speed is the case where the brochure figure is roughly achievable.
Cost per mile is the number worth carrying away. It turns a journey into a comparison you can make against a train ticket, a colleague splitting the drive, or simply not going.
What it works out
- Total fuel cost, one way and there and back
- How much fuel the journey burns
- Cost per mile or per kilometre
- Miles per gallon, US or imperial, or litres per 100km
The formula
Fuel used = Distance ÷ Economy Cost = Fuel used × Price
Divide the distance by the economy to get the fuel, then multiply by the price. On 300 miles at 32 mpg that is 9.375 gallons, and at $3.40 a gallon the journey costs $31.88.
On metric the division goes the other way, because litres per 100km is fuel per distance rather than distance per fuel. Multiply the distance by the consumption and divide by 100: 480km at 7.35 L/100km is 35.3 litres.
That difference is not a quirk of notation. Miles per gallon is a reciprocal measure, and it is why equal-looking improvements are not equal savings. Going from 10 to 15 mpg saves twelve times as much fuel over the same distance as going from 40 to 45 does.
Cost per mile is the total divided by the distance, and on these figures it comes to about 11 cents. It is the number that makes a journey comparable to anything else.
- Distance
- The whole journey. Double it for a return trip, or use the figure the tool gives for there and back.
- Economy
- What the vehicle actually returns, which is usually a little worse than the brochure figure.
- Price
- What you pay at the pump, per gallon or per litre.
A worked example
A 300 mile drive in a car returning 32 mpg, with fuel at $3.40 a gallon.
That works out to $31.88 .
- Fuel used
- 9.38 gallons
- Cost per mile
- $0.11
- There and back
- $63.75
- Fuel there and back
- 18.75 gallons
Questions
How do I work out the fuel cost of a trip?
Divide the distance by the miles per gallon to get the gallons, then multiply by the price. A 300 mile trip at 32 mpg uses 9.375 gallons, which at $3.40 a gallon is $31.88.
What fuel economy figure should I use?
The one your own vehicle returns, measured from a couple of fill-ups, rather than the brochure number. Real-world economy is usually a few per cent worse, and considerably worse on short journeys from cold.
Why does the same car have two different mpg figures?
Because a US gallon and an imperial gallon are not the same size — 3.785 litres against 4.546. A car returning 32 mpg in the US is 38.4 mpg in the UK. The fuel used is identical; only the unit changed.
Does driving faster use more fuel?
Above roughly 55 to 60 mph, yes, and sharply. Air resistance rises with the square of speed, so most cars are noticeably thirstier at 80 than at 65 — often by a fifth or more.
Is the fuel cost the real cost of the journey?
No, and it is usually about a third of it. Tyres, servicing, insurance and depreciation are all bought by the mile even though they are not paid for at the pump, which is why mileage reimbursement rates are several times the fuel cost.
How much does air conditioning cost in fuel?
Very roughly five to ten per cent in town, and less on a motorway. Open windows at speed cost about as much through drag, so the choice matters less than it is often said to.
Does a roof box make much difference?
More than most people expect — commonly ten to twenty-five per cent at motorway speed, because it spoils the airflow over the roof. Empty roof bars alone still cost a few per cent, so taking them off between trips is worth doing.
Should I split the cost with passengers?
That is a matter for you, but the fair figure is usually more than the fuel. The trip cost calculator splits fuel, tolls and parking between however many people are in the car.