Fuel consumption calculator

Two uses: measure consumption or plan a trip

The calculator needs the litres used. To find your car's real consumption, measure tank to tank: fill up completely, reset the trip meter, drive as usual and fill up completely again. The litres from the second fill and the kilometres on the trip meter are your inputs.

If you are only planning a trip, work out the litres first: litres = consumption (l/100 km) × kilometres ÷ 100. Enter that figure with the distance and price to get the trip cost.

Example: Tallinn-Tartu and back

Tallinn to Tartu is roughly 185 km by road, so about 370 km there and back. Assume the car uses 6 l/100 km and fuel costs 1.65 €/l. These are example figures, not today's price or your car's actual consumption.

Litres: 6 × 370 ÷ 100 = 22.2 l. Enter 370 km, 22.2 l and 1.65 €/l. The calculator shows a cost of 36.63 €, 9.90 € per 100 km and 0.10 € per km. With three people sharing costs, that is 12.21 € each.

If the same car uses 7 l/100 km in winter or at higher speed, it needs 25.9 litres and the trip costs 42.73 €. One extra litre per hundred kilometres adds 6.10 € to this trip.

Example: Tallinn-Pärnu and city driving

Tallinn to Pärnu is roughly 130 km. At 6 l/100 km one way takes 7.8 l, which costs 12.87 € at 1.65 €/l. The 260 km round trip needs 15.6 l and costs 25.74 €.

Short city trips usually push consumption up. If you drove 40 km during a week and refilled 3.6 l, the calculator shows 9 l/100 km, a cost of 5.94 € and 14.85 € per 100 km. The same car can have a very different cost per kilometre on the highway and in town.

Common measuring mistakes

The consumption formula is simple, but input errors easily distort the result. Over a short distance even a one-litre error makes a big difference.

• The tank is not filled the same way both times: the nozzle's first automatic cut-off is not always the same level, so fill up consistently.
• The distance measured is too short. The longer the distance between two fills, the smaller the effect of a one-litre inaccuracy.
• The trip computer reading is taken as fact. It is an estimate worth checking now and then with the tank-to-tank method.
• Mixing up l/100 km and km/l. They are reciprocals: 6 l/100 km means 100 ÷ 6 = 16.67 km per litre.
• Trusting the cost per km too much. It is rounded to the cent, so 9.90 € and 11.55 € per 100 km show as 0.10 € and 0.12 €. Compare the cost per 100 km instead.

Electric cars and other special cases

The maths works for an electric car too if you enter kilowatt-hours instead of litres and the kWh price instead of the fuel price. For example, 20 km, 4.2 kWh and an assumed 0.25 €/kWh give 21 kWh/100 km, a cost of 1.05 € and 5.25 € per 100 km. Charging losses are not included.

The calculator counts fuel only. A car's true cost per kilometre also includes servicing, tyres, insurance and depreciation, so fuel is just one part of the total.