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.

How do I work out fuel cost per mile?

Divide the price of a gallon by the mpg: at 3.50 a gallon and 30 mpg, fuel costs 3.50 ÷ 30 = 0.1167 a mile. For a car rated in L/100km, multiply the L/100km by the price of a litre and divide by 100 for the cost per km. The Per mile and per km row gives both for whatever you enter, in any mix of units.

Can I do this in Excel or Google Sheets?

Yes, for one set of units: =distance/mpg*price gives the trip cost from miles, mpg and a price per gallon, and =distance*L_per_100km/100*price does the same in kilometres and litres. Mixing units is where a spreadsheet needs the conversion constants, and this page writes them into the working: 1.609344 km to the mile, 3.785411784 litres to the US gallon and 4.54609 to the UK one.

Can I compare two cars?

Yes. Switch on Second vehicle and enter the other car's fuel economy. The Difference row shows how much more or less it costs over the same trip, in money and as a percentage. Give the second vehicle its own price to compare diesel against petrol.

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.

Does it work for diesel, a truck, an RV or a motorhome?

Yes. The sum depends only on how far the vehicle goes on a gallon or a litre and what the fuel costs, so it works for petrol, gasoline, diesel, LPG, a hybrid, a van, a moving truck, an RV or a motorhome. Enter that vehicle's own figure, and when towing a trailer, the economy you see while towing. It does not price electricity, so it cannot work out what an electric car costs to charge.

Which units suit the UK, Europe, Canada or India?

UK drivers usually want miles, mpg UK and a price per litre. Most of Europe, Canada and Australia rate cars in L/100km and price fuel per litre, and km/L is common in India. Each set of buttons is independent, so any combination works.

Does it work out the distance from a map?

No. It does not plan routes, so it cannot look up how far a journey is or add tolls. Take the distance from a route planner or your odometer and enter it here.

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.

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 cost35.0010 US gal over 300 miles

Distance

Efficiency

Measured in

Fuel price

Quoted

Sharing

Trip

Round trip

Compare

Second vehicle

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.

Fuel neededone way
10 US gal (37.854 L)
Total costfuel only, no tolls or parking
35.00
Per personone person
35.00
Per mile and per kmthe same money over two rulers
0.1167 per mile, 0.0725 per km
The workingevery conversion, in full
300 mi ÷ 30 mpg = 10 US gal; 10 US gal × 3.50 = 35.00

Two gallons, and one unit that runs backwards. Choose the gallon used by your fuel price and efficiency figure. L/100km measures fuel per distance, so a lower number means less fuel used, 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.
How do I work out fuel cost per mile?: Divide the price of a gallon by the mpg: at 3.50 a gallon and 30 mpg, fuel costs 3.50 ÷ 30 = 0.1167 a mile. For a car rated in L/100km, multiply the L/100km by the price of a litre and divide by 100 for the cost per km. The Per mile and per km row gives both for whatever you enter, in any mix of units.
Can I do this in Excel or Google Sheets?: Yes, for one set of units: =distance/mpg*price gives the trip cost from miles, mpg and a price per gallon, and =distance*L_per_100km/100*price does the same in kilometres and litres. Mixing units is where a spreadsheet needs the conversion constants, and this page writes them into the working: 1.609344 km to the mile, 3.785411784 litres to the US gallon and 4.54609 to the UK one.
Can I compare two cars?: Yes. Switch on Second vehicle and enter the other car's fuel economy. The Difference row shows how much more or less it costs over the same trip, in money and as a percentage. Give the second vehicle its own price to compare diesel against petrol.
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.
Does it work for diesel, a truck, an RV or a motorhome?: Yes. The sum depends only on how far the vehicle goes on a gallon or a litre and what the fuel costs, so it works for petrol, gasoline, diesel, LPG, a hybrid, a van, a moving truck, an RV or a motorhome. Enter that vehicle's own figure, and when towing a trailer, the economy you see while towing. It does not price electricity, so it cannot work out what an electric car costs to charge.
Which units suit the UK, Europe, Canada or India?: UK drivers usually want miles, mpg UK and a price per litre. Most of Europe, Canada and Australia rate cars in L/100km and price fuel per litre, and km/L is common in India. Each set of buttons is independent, so any combination works.
Does it work out the distance from a map?: No. It does not plan routes, so it cannot look up how far a journey is or add tolls. Take the distance from a route planner or your odometer and enter it here.
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.