Fuel Cost Calculator

How it works

The cost of a trip is the fuel it burns multiplied by the price of that fuel. The calculator works in either metric or imperial units, chosen by your region and changeable at the top.

Metric (kilometers, liters):

fuel used (L) = distance (km) × consumption (L/100 km) / 100
cost = fuel used × price per liter

Imperial (miles, US gallons):

fuel used (gal) = distance (miles) / fuel economy (mpg)
cost = fuel used × price per gallon

The result also shows the cost per kilometer or per mile, the figure that makes trips and cars comparable regardless of distance.

The price is handled as whole cents internally, not decimals. The fuel quantity is worked out to a millionth of a liter or gallon, which is finer than any pump, and the cost is then rounded once to the nearest cent (a tie rounds up). The cost per distance is calculated from the fuel per kilometer or mile, not by dividing the rounded total, so it stays accurate for short trips too.

Cost per trip or cost per kilometer

The cost per kilometer is shown rounded to a cent, like every other money figure. That is fine for comparing cars, but do not multiply it by a long distance to get the trip cost. At 6.3 L/100 km and 1.80 per liter the exact figure is 6.3 × 1.80 / 100 = 0.1134 per km, which is displayed as 0.11. Multiplying 0.11 by 250 km gives 27.50, while the real trip cost is 28.35. Use the total the calculator gives you for the trip, and the per-km figure for comparisons.

Round trips

Enter the full distance there and back. 250 km each way is 500 km: 500 × 6.3 / 100 = 31.5 L, and at 1.80 per liter that is 56.70, exactly twice the one-way 28.35. If the way back differs (a steep climb one way, a heavy load only on the way out), run the two legs separately with their own consumption and add them.

Electric cars

The same formula works with kWh in place of liters. In the metric mode, enter the distance, the consumption in kWh per 100 km in the consumption field and the price of one kWh in the price field. 250 km at 18 kWh/100 km uses 250 × 18 / 100 = 45 kWh; at 0.30 per kWh that is 13.50, or 0.054 per km (shown rounded). In the imperial mode the consumption field takes miles per kWh: 200 miles at 3.5 miles/kWh is 200 / 3.5 = 57.14 kWh, and at 0.15 per kWh the cost is 8.57. The labels and units on the page still say liters and gallons; ignore them and read the result as kWh. Charging from a home socket or a public charger can use more energy at the wall than the car's display reports, because of charging losses, so base the consumption on what the meter or charger recorded if you can. The prices in these examples are illustrative.

Cars with two fuels

For a car that runs on LPG and petrol, calculate each fuel on its own distance and add the two. Say a 400 km trip with 300 km on LPG at 10 L/100 km (LPG at 0.90 per liter) and 100 km on petrol at 7 L/100 km (petrol at 1.80 per liter):

LPG:    300 × 10 / 100 = 30 L   × 0.90 = 27.00
petrol: 100 × 7 / 100  =  7 L   × 1.80 = 12.60
total:  39.60, or 0.099 per km over 400 km

Use the consumption you measured on each fuel, as the same car usually burns a different volume of each.

L/100 km, mpg (US) and mpg (UK)

The imperial mode uses the US gallon (3.785 liters). A UK gallon is 4.546 liters, so a UK "40 mpg" is not 40 in the calculator. Convert first: 40 UK mpg ≈ 40 × 0.8327 = 33.3 mpg (US), or 282.481 / 40 = 7.06 L/100 km, which you can enter in the metric mode with the price per liter. Then 300 miles is 482.8 km, and the fuel is 482.8 × 7.06 / 100 = 34.1 L, which matches 300 / 40 = 7.5 UK gallons × 4.546 L.

What moves consumption

The consumption you enter is an average for one kind of driving. Higher speeds, short trips from a cold engine, heavy traffic, hills, a full car, a roof box, air conditioning or heating, low tire pressure and cold weather all push consumption up, and an electric car's range reacts to cold and speed in the same way. This is why a number measured on your commute is a good guide to that commute and a rougher guide to a holiday drive with a loaded car.

Examples

Metric. A 100 km trip at 7 L/100 km burns 7 L. At 4.00 per liter that is 28.00, or 0.28 per km.

A real-world trip. 250 km at 6.3 L/100 km needs 15.75 L. At 1.80 per liter the cost is 28.35.

Imperial. 300 miles at 30 mpg burns 10 gallons. At 3.50 per gallon the cost is 35.00, or 0.12 per mile.

Comparing two cars. You drive 15,000 km a year at 1.80 per liter. Car A uses 7 L/100 km: 1,050 L, or 1,890 a year. Car B uses 9 L/100 km: 1,350 L, or 2,430 a year. Two liters per 100 km is a difference of 540 a year.

Things to watch for

• Use real consumption. The figure from the brochure comes from a laboratory test. Your own measured figure is the one that predicts your bill.
• Prices change. Fuel prices move by the week and differ by station and motorway. Use the price you will actually pay, and re-run the calculation if it changes.
• Driving style matters. Motorway speed, city traffic, hills, a full car and the air conditioning all change consumption. A trip on a different road may not match the figure you measured on your commute.
• It is fuel only. Tolls, parking, ferries and the wear on the car are not included.
• Splitting the cost. If you share the trip, divide the total fuel cost the calculator gives by the number of people. Do not divide the cost per km, which is for the whole vehicle.
• Check the unit before you type. A figure in L/100 km, km/L, mpg (US) or mpg (UK) means four different things. A smaller L/100 km is better, a larger mpg is better, and entering one in the field meant for the other gives a nonsense cost.
• The result is an estimate. It is a calculation from the numbers you give it, for information only, not a quote of what you will pay at the pump.
• Everything runs in your browser. The numbers you enter are not sent to a server.

To measure your own consumption, use the fuel consumption calculator; for other unit changes, the unit converter.