A simple formula is all you need to quickly calculate the energy consumption of your household appliances.
What information do you need?
To calculate the electricity consumption of an appliance, you need 3 things:
- The power of the appliance, expressed in watts
- The number of hours per day that the appliance is in use
- The number of days per year that the appliance is in use
The power rating can usually be found on the appliance itself, on the energy label or in the manual.
How do you calculate consumption?
Electricity consumption is expressed in kilowatt hours (kWh). The calculation is as follows:
[number of hours per day] × [number of days per year] × [power in watts] ÷ 1,000 = consumption in kWh
By dividing the power by 1,000, you convert watts to kilowatts. This gives you the annual consumption in kWh.
Some examples
Consumption of an LED lamp
Suppose you use an LED bulb in your living room.
You use the bulb:
- 3 hours a day
- for 330 days a year
- with a power of 6 watts
- The consumption is then: 3 × 330 × 6 ÷ 1,000 = 6 kWh per year
That amounts to approximately €2 per year, all inclusive (in January 2026).
How can I track my electricity consumption for each device separately?
Consumption of a vacuum cleaner
In this example, we use a vacuum cleaner:
- 2 hours per day
- For 52 days a year (once a week)
- with a power of 600 watts
- The consumption is then: 2 × 52 × 600 ÷ 1,000 = 62 kWh per year
That amounts to approximately €20 per year, all inclusive (in January 2026).
Did you know?
A vacuum cleaner with a clogged bag or filter can lose up to 50% of its suction power, while consuming the same amount of electricity.
Consumption of a fridge with freezer
Let's now look at the specific case of a fridge with freezer compartment. Although it runs 24 hours a day, all year round, the motor (the compressor) does not run continuously. It stops as soon as the desired temperature is reached. For a class E or F model:
- 8 hours per day (the compressor does not run continuously)
- For 365 days a year
- with a power rating of 100 watts
- The consumption is then: 8 × 365 × 100 ÷ 1,000 = 292 kWh per year
That amounts to approximately €90 per year, all inclusive (in January 2026).
This example shows how quickly consumption can increase for frequently used appliances, even at average power levels.
Did you know?
A poorly defrosted freezer is one of the biggest invisible energy wasters in the home. The ice that accumulates on the walls acts as an insulating barrier: it prevents the transfer of cold between the cooling circuit and the air inside. Just 3 mm of ice can increase electricity consumption by around +30%.
Heat pump consumption
Let's now look at a 'classic' heat pump (air/air or air/water) used to heat a well-insulated 100 m² house (excluding domestic hot water).
- 7.2 hours per day
- For 210 days a year (from October to April)
- with a capacity of 2,300 watts (8,000 watts with a COP of 3.5)
- Consumption is then: 7.2 × 210 × 2,300 ÷ 1,000 = 3,478 kWh per year
That amounts to approximately €1,200 per year, all inclusive (in January 2026).
Did you know?
Although the price per kWh of electricity is higher than that of gas, a heat pump uses 75% free energy from the environment. By switching from a gas boiler to a heat pump, final energy consumption can be reduced by a factor of 3 or 4 under favourable conditions. However, keep in mind that good insulation (good EPB class) is necessary to achieve such a ratio.
Would you like to estimate your electricity consumption even more accurately? It may help to compare the consumption of your various appliances side by side.