What this tool does
The calculator divides the distance by your car's fuel economy to find how much fuel the trip uses, then multiplies by the price you pay at the pump. It works in four unit systems: miles with US mpg and a price per gallon, miles with UK mpg and a price per litre (the way British drivers see both numbers), and kilometres with litres per 100 km or with km per litre.
Tap Round trip to double the distance, enter how many times you make the journey to cost a month of commuting, and add tolls or parking. You get the total, the fuel used and the cost per mile or kilometre.
Enter the number of people in the car to split the bill. Shares can be rounded up to 10 cents, 1 or 5 so nobody comes up short, and the page shows how much is collected and how much is left over. You can also leave the driver out of the split. The result can be copied as plain text or printed on one page for an expense claim.
How to use it
- Choose your units and currency symbol, then enter the one-way distance and pick One way or Round trip.
- Enter your car's fuel economy and today's fuel price. Both are remembered on this device for next time.
- If you make the same trip several times, enter how many; add any tolls or parking for one trip.
- Enter how many people are sharing and how to round each share, then press Copy result to paste it into a message, or Print for a one-page record.
How the cost is worked out
Fuel used is distance ÷ fuel economy (or distance × L/100 km ÷ 100), and the cost is fuel used × price. A 250-mile trip at 28 mpg uses 8.93 gallons; at $3.15 a gallon that is exactly $28.125, which rounds to $28.13. The page reads every number you type as an exact decimal and does the sums in whole numbers, so a result that lands on half a cent is never rounded the wrong way by floating-point error.
UK mpg is not US mpg
A UK gallon is 4.54609 litres and a US gallon 3.785 litres, so 40 mpg on a British dashboard means more distance per gallon than 40 mpg on an American one. Many calculators treat every mpg as US gallons. For 300 miles at 40 mpg with fuel at 1.45 a litre, the UK setting gives 34.10 litres and 49.44, where a US-gallon calculator says 28.4 litres and about 41.17, roughly 17 percent too low.
Splitting the bill fairly
If $28.13 is shared by two people, each share is $14.065, so with exact cents each pays $14.07 and one cent is left over. Rounding up to a dollar makes paying back easier: each pays $15 and $1.87 is left, usually kept by whoever paid at the pump. Untick 'The driver pays a share too' if passengers are covering the fuel; four people in the car then means three shares.
The figure is an estimate. Real fuel economy changes with traffic, speed, weather, load and driving style, so a cautious budget allows a little extra.
Your data
The distances and prices you enter are worked out inside this browser and never sent anywhere. Your fuel economy, fuel price and settings are kept on this device for next time; distance, trip count, tolls and the number of people are not.
Questions and answers
Should I enter tolls for both directions?
Enter what one trip costs in tolls and parking. For a round trip, add the tolls for both directions together. If you set a number of trips, the amount is multiplied by it.
Why do the shares add up to more than the total?
When the total does not divide evenly, each share is rounded up so nobody pays too little. Exact cents leave at most a few cents over; rounding to 1 or 5 is easier to pay back but leaves more. The leftover is shown under the result.
Which fuel economy number should I use?
Your car's trip computer or the average shown on the dashboard is closest to real driving. Official ratings are measured under test conditions and are usually higher than what you get in traffic or in winter.
Can I use it for business mileage claims?
You can print the calculation as supporting detail. Many employers and tax authorities reimburse a fixed rate per mile or kilometre instead of actual fuel, so check which rule applies before you claim.
Does it work for diesel or electric cars?
For diesel or LPG, enter that car's economy and that fuel's price and the sum is the same. Electric cars are measured in kWh rather than litres or gallons, so this page does not cover them.
