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Fuel Consumption Calculator

How many litres does your car use per 100 kilometres — and how far does it go on one litre? Enter the kilometres driven and the litres you filled to measure real consumption, the cost per kilometre and the range on a full tank.

Fill the tank, drive, fill it again and note the kilometres and the litres of that second fill-up. For example, 500 km on 35 litres is 7 l/100 km, or 14.29 km per litre. The tank size and the manufacturer figure are optional.

Real consumption
7 l/100 km
Kilometres per litre
14.29 km/l
Cost per 100 km
€12.60
Cost per km
0.126 €/km
Kilometres per euro
7.9 km
Range on a full tank
714 km

Educational estimate, not financial advice. Consumption measured over a single tank varies with the route, driving style and traffic; repeat the measurement over several tanks for a reliable figure.

1

The consumption sum, in both units

Consumption in litres per 100 km is the litres used divided by the kilometres driven, times 100. Over 500 km on 35 litres: 35 ÷ 500 × 100 = 7 l/100 km. The other way of saying the same thing is kilometres per litre, which is the division the other way round: 500 ÷ 35 = 14.29 km/l. The two units are reciprocal (km/l = 100 ÷ l/100 km), and this calculator always shows both, because the car’s spec sheet speaks in l/100 km while the question is usually asked in kilometres per litre.

2

How to measure properly: full tank to full tank

The measurement is only reliable if the litres match the kilometres exactly. The method is simple: fill the tank to the brim, reset the trip meter, drive normally and, at the next stop, fill it to the brim again. The litres of that second fill-up are precisely what you used over the distance on the trip meter. If you do not brim the tank both times the result is wrong — and a single tank only reflects the driving you did on that tank, so it is worth repeating the measurement over several tanks.

3

Cost per kilometre and per 100 km

With the price per litre, consumption turns into money. The cost per 100 km is the consumption times the price: 7 l/100 km at €1.80 a litre is €12.60 for every 100 km. The cost per kilometre is the same figure divided by 100, about €0.126/km. And kilometres per euro answers the question the other way round: if 500 km cost €63, each euro buys nearly 8 kilometres, so €20 takes you about 159 km.

4

Real consumption against the manufacturer figure (WLTP)

The spec-sheet value is the combined consumption measured on the WLTP cycle, under standardised laboratory conditions. Real consumption depends on driving style, speed, traffic, load, air conditioning and tyres, which is why it usually sits above the homologated figure. If you enter the spec-sheet consumption, the calculator shows the difference in litres per 100 km and as a percentage — the comparison that tells you whether the car is behaving as expected or whether something is worth checking.

5

Range on a full tank

Once you know the real consumption and the tank capacity, the range is a multiplication: kilometres per litre times the litres in the tank. At 14.29 km/l, a 50-litre tank gives about 714 km from full. That is an estimate from a completely full tank at the consumption you have just measured: in practice leave a margin, because the reserve is not meant to be run dry and consumption rises on the motorway.

Worked example

Say you brimmed the tank, reset the trip meter and, 742 km later, filled it again with 41.3 litres at €1.759 a litre. Real consumption is 41.3 ÷ 742 × 100 = 5.57 l/100 km, the same as 17.97 km per litre. That fill-up cost €72.65, which works out at €0.098 per kilometre and €9.79 per 100 km — each euro of diesel returned 10.2 km. With a 55-litre tank, the range at this consumption is about 988 km. And if the car’s spec sheet says 4.9 l/100 km, you are using 0.67 l/100 km more than the homologated figure, roughly 13.6% above it.

Frequently asked questions

How do you calculate fuel consumption?
Divide the litres used by the kilometres driven and multiply by 100. For example, 35 litres over 500 km is 35 ÷ 500 × 100 = 7 litres per 100 km. For the measurement to be right, the litres must come from a fill-up that brims the tank, after having brimmed it at the start of the stretch.
How far does a car go on 1 litre of petrol?
It depends on the car’s consumption, and the sum is the division the other way round: kilometres divided by litres. A car doing 7 l/100 km covers 14.29 km on a litre; at 5 l/100 km it does 20 km, and at 10 l/100 km it does 10 km. The general rule is 100 divided by the consumption in l/100 km.
How many kilometres will €20 of diesel take me?
Divide the €20 by the price per litre to get the litres, then multiply by the kilometres per litre. With diesel at €1.75, €20 buys 11.4 litres; in a car doing 14.29 km/l that is about 163 km. The calculator shows the kilometres per euro directly.
Why is real consumption higher than the manufacturer figure?
Because the spec-sheet value comes from the WLTP test cycle, under standardised conditions, and real driving has variables the test does not reproduce: speed, braking, traffic, gradient, load, air conditioning, tyres and temperature. The homologated figure exists to compare cars with each other on equal terms, not to predict your consumption.
Can I use the figure from the trip computer?
As an indication, yes. But the hand calculation is the reference, because it uses the litres you actually paid for at the pump and the kilometres you actually drove, whereas the trip computer estimates fuel flow. If the two disagree consistently, the tank-to-tank measurement is the one that counts.
Does this calculator work for an electric car?
No. An electric car is measured in kilowatt-hours per 100 km and paid for at an electricity tariff, not by the litre. For that calculation see the electric-car charging cost calculator.

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Author: Thorben Rasmus Idel · Reviewed by: Nahar Geva · Last reviewed: