Fuel Cost Calculator
Result
Fuel cost for the trip
- Fuel used (US gallons)
- 3.33 gal (US)
- Fuel used (liters)
- 12.62 L
- Cost per mile
- 0.12
- Cost per 100 kilometers
- 7.25
A fuel cost calculator takes the four numbers a trip is actually made of — how far you are going, how much fuel the car uses, what the pump charges, and what unit that price is quoted in — and returns what the drive costs. It is a multiplication, not an estimate: distance ÷ fuel economy gives the gallons burned, and gallons × price per gallon gives the money. The reason it is worth a page rather than a mental sum is that the four numbers arrive in units that do not match. Distance might be in miles while the price is per liter, or the fuel economy might be quoted in liters per 100 km while the pump sells gallons. Each of those mismatches has a conversion factor hiding in it, and the imperial gallon — 4.54609 liters against 3.785411784 — is the one that quietly moves a figure by 20%. The result is given as a plain number: read it in whatever currency your pump quotes, because the arithmetic is identical in all of them. Alongside the total you get the fuel used in both gallons and liters, plus the cost per mile and the cost per 100 km so the trip can be compared with another route or another car.
Formula
trip cost = (distance ÷ mpg) × price per gallon
- distance
- Length of the trip, in miles
- mpg
- Fuel economy, in miles per US gallon
- price per gallon
- Pump price, converted to your currency's price for one US gallon
Use it before a long drive to compare two routes, or after one to see what the journey actually cost. If the fuel economy on the window sticker is the only figure you have, the answer is a plan rather than a measurement — real fuel economy on a motorway at a steady speed beats the certified figure, and short cold trips in town fall well below it.
Worked examples
100 miles at 30 mpg, fuel at 3.50 a gallon
- Distance: 100 miles
- Fuel economy: 30 mpg
- Fuel burned: 100 ÷ 30 = 3.33 US gallons
- In liters: 3.33 × 3.785411784 = 12.62 L
- Cost: 3.33 × 3.50 = 11.67
- Per mile: 11.67 ÷ 100 = 0.12
- Per 100 km: the trip is 160.93 km, so 11.67 ÷ 160.93 × 100 = 7.25
The price is per US gallon here, which is what a pump in the United States charges. A pump in Britain sells liters, and Canada quotes cents per liter too, so the fourth input exists precisely so you do not have to convert the price in your head before typing it.
300 miles at 7.5 L/100 km, fuel at 1.60 a liter
- Distance: 300 miles = 300 × 1.609344 = 482.80 km
- Fuel economy: 7.5 liters per 100 km
- Fuel burned: 482.80 ÷ 100 × 7.5 = 36.21 L
- In US gallons: 36.21 ÷ 3.785411784 = 9.57 gal
- Cost: 36.21 × 1.60 = 57.94
- Per 100 km: 57.94 ÷ 482.80 × 100 = 12.00
- Per mile: 57.94 ÷ 300 = 0.19
Two different unit families meet in this one: the distance is in miles and the economy is metric. That is the normal case rather than the odd one — a driver in Britain buys fuel by the liter, thinks about economy in miles per gallon, and measures distance in miles, all at once.
Limitations
The arithmetic is exact and the inputs are not. Fuel economy varies with speed, load, temperature and how hard the accelerator is pressed, so a trip costed from a single economy figure is a planning number; the same car on the same route in winter will burn noticeably more. The price is whatever you typed — pump prices differ between towns and change weekly, and the result is only as current as that input. Nothing here accounts for the fuel burned while the engine idles in traffic, the extra consumption of a cold engine on a short trip, or a roof box. The output is a number without a currency symbol, so it is correct in your currency and meaningless in anyone else's. Finally, this page costs one trip. The cost of owning the car — insurance, depreciation, servicing, tyres — is several times the fuel bill and is not in here.
Frequently asked questions
- How do I work out the fuel cost of a trip?
- Divide the distance by the fuel economy to get the fuel burned, then multiply by the price. A 100 mile trip at 30 mpg burns 100 ÷ 30 = 3.33 gallons, and at 3.50 a gallon that is 11.67. That is the whole calculation — everything else on this page is a unit conversion wrapped around it.
- How do I get the cost per mile?
- Divide the trip cost by the distance in miles: 11.67 over 100 miles is 0.12 a mile. It is the more useful figure of the two when you drive the same route regularly, because it stays comparable when the distance changes — the cost per 100 km is the same number in metric clothing, and the page gives both.
- Which gas price should I enter?
- Whatever you last paid, in the unit the pump quotes — the fourth input lets you say whether that is per gallon, per imperial gallon or per liter, so no conversion by hand is needed. Do not average several prices: the point of the figure is what the trip will cost at the price you will actually pay.
- Why is there no currency in the answer?
- Because the page does not know which one you mean, and a wrong symbol is worse than none. The multiplication is the same in dollars, euros, pounds or yuan, so the number is correct in whatever currency you typed the price in. Read it as your own money.
- Does a different fuel economy unit change the answer?
- No — 30 mpg and 7.84 liters per 100 km are the same car, and the trip costs the same either way. What changes the answer is the unit of the price, because that one is not a description of the car but of the transaction at the pump, and a price per imperial gallon is about 20% higher in number than the same fuel priced per US gallon.
References
- Gasoline and Diesel Fuel Update — U.S. Energy Information Administration
- Fuel Economy — U.S. Department of Energy and Environmental Protection Agency