Fuel Cost Calculator
Work out what a trip costs in fuel from three numbers, each in whatever unit it was quoted in: miles or kilometres, mpg or L/100km or km/L or imperial mpg, and a price per US gallon, per litre or per imperial gallon. Every conversion the answer needs is written into the working with the constant it used, so mixing a car rated in mpg with a distance in kilometres and a price in litres takes no arithmetic on your part.
One way fuel cost10 US gal over 300 miles
Enter the price in whatever currency you buy fuel in. The answer comes back in the same one, because the arithmetic never touches an exchange rate.
Two gallons, and one unit that runs backwards. The US gallon is 3.785411784 L and the imperial gallon is 4.54609 L, so the same car is 40 mpg in Britain and 33.3 mpg in the States. L/100km is the opposite measure again: it is fuel per distance, so a lower number is a better car, and it multiplies where mpg divides. Every conversion the answer needs is written into the working above with the constant it used, so you can check which gallon went where.
Common questions
- How do I convert mpg to L/100km?
- They run in opposite directions, which is why the conversion is a division rather than a scaling: L/100km = 235.215 / mpg for US mpg, and 282.481 / mpg for imperial. A higher mpg is a better car; a higher L/100km is a worse one. You do not have to do it by hand here, because the tool takes either unit directly and converts the distance for you: pick L/100km and enter the number printed on a European spec sheet, or pick mpg and enter the one on a US window sticker.
- Is a UK gallon the same as a US gallon?
- No, and the gap is about 20%. The US liquid gallon is exactly 3.785411784 litres; the imperial gallon is exactly 4.54609 litres. So the same car is 40 mpg in Britain and 33.3 mpg in the States, and a price quoted per gallon means different money on each side of the Atlantic. The tool keeps them apart: there is an mpg UK option for efficiency and a per UK gallon option for price, and the working names which gallon it used at each step.
- How do I split fuel costs between passengers?
- Set the number of people sharing and the total is divided by it. Fuel needed, cost per mile and cost per km are unaffected, because who pays does not change what the car burns. The split is a straight division: four people sharing a 35.00 tank each owe 8.75. If a passenger joins part way, run the trip as two legs and split each one on its own.
- Does it handle round trips?
- Yes. Switch on Round trip and the distance you entered is doubled before anything else happens, so the fuel and the total both double. Cost per mile and cost per km stay exactly where they were, because those are rates rather than totals, and the working shows the doubling as its first step so you can see which distance the rest of the sum used.
- What currency does it use?
- Whichever one you type. The price is a plain number with no currency attached, and the answer comes back in the same units you put in, because the arithmetic never touches an exchange rate. Enter 3.50 for dollars a gallon or 1.45 for pounds a litre and read the total the same way.
- Why is my real fuel cost higher than this?
- The sum is exact on the numbers you enter, but the mpg figure on a spec sheet is measured on a test cycle, and real driving is not one. Motorway speed, a full car, a roof box, cold weather, short trips from cold and heavy traffic all push consumption up, often by 10 to 30 percent. Enter the efficiency you actually see on the trip computer rather than the advertised one and the total will track much closer.
Exact arithmetic on the numbers entered: distance divided by efficiency, times price. Real consumption varies with speed, load and weather, so treat the result as the figure your own inputs imply.