Fuel or electricity is the energy part of your cost per km. With the same consumption, a higher price increases the cost of each km and the monthly total.
The calculation, step by step
- Consumption: use L/100 km for a fuel-powered car or kWh/100 km for an electric car.
- Energy per km: divide consumption by 100 and multiply by the price in €/L or €/kWh.
- Monthly energy: multiply that cost per km by your monthly work km, including the drive to passengers.
If you use km/L, mpg or mi/kWh, divide the price by consumption. The result is per km or per mile, depending on the unit; with mpg, the price is per gallon.
Two examples
For a fuel-powered car with 6 L/100 km at €1.80/L, the maths is 6 ÷ 100 × 1.80 = €0.108/km. For an electric car with 16 kWh/100 km at €0.25/kWh, it is 16 ÷ 100 × 0.25 = €0.04/km.
Use the same km as in the cost per km article: five days a week, 200 km a day. The average month has 5 × 200 × 52 ÷ 12 ≈ 4,333.33 km.
| Example | Consumption | Price | Energy per km | Energy per month |
|---|---|---|---|---|
| Fuel-powered | 6 L/100 km | €1.80/L | €0.108000 | €468.00 |
| Electric | 16 kWh/100 km | €0.25/kWh | €0.040000 | €173.33 |
All figures are fictional examples, not market prices or spending forecasts. The month is an average; calculations use unrounded values, including monthly km. The per km column uses six decimal places.
The calculator shows €0.11/km for the fuel-powered example and €0.04/km for the electric one. Money is rounded to six decimal places, then to two for display. To calculate the month, use the cost per km before rounding.
If the price rises
Keep the same 6 L/100 km and change only the price from €1.80 to €2.00/L. Energy now costs 6 ÷ 100 × 2.00 = €0.120/km. The difference is 0.120 minus 0.108 = €0.012/km.
For the same 4,333.33 km per month, energy rises from €468.00 to €520.00, an extra €52.00. If you keep the €130.00 in fixed costs from the cost per km article, total car costs rise from €598.00 to €650.00 per month. With the same amount received, you have €52.00 less left, as in the what is left calculation.
The logic is the same for an electric car: with the same consumption and km, a change in price per kWh changes cost per km and the monthly total. These figures are still fictional.
Use the price you actually pay
Enter the price you pay per litre or per kWh, including the discounts and charges that actually apply to you. If you refuel or charge at different prices, divide the total paid by the corresponding litres or kWh to find the average price.
Count energy once, through consumption and price. Don't repeat it under “Other”. The result is an estimate: redo the maths when your price, consumption or work km change.
Use your own numbers
In Radr's fuel and charging calculator, enter distance, consumption and price. To include maintenance, insurance and other car costs, use Full cost.
General information, not tax or legal advice.
