Step 1: find the electrical input
Look for watts (W) on the appliance label or manual. Be careful not to confuse output capacity with electrical input — this matters especially for heaters, air conditioners and chargers.
Step 2: calculate kilowatt-hours
Use watts ÷ 1,000 × hours. For example, 2,000 W for 3 hours equals 6 kWh if the device draws 2,000 W continuously.
Step 3: multiply by your tariff
Multiply kWh by the energy price from your tariff. At €0.30/kWh, 6 kWh costs €1.80 in usage charges.
Step 4: improve the estimate
For thermostatic or variable-load devices, use measured average power or measured kWh over a representative session. For time-of-use tariffs, split usage across each price period.
What not to mix into an appliance comparison
Fixed standing charges or subscription fees usually do not change when one appliance runs for an extra hour. Keep them separate when comparing the variable cost of two devices.