For a flat-rate estimate, electricity cost = power (W) × runtime (hours) ÷ 1,000 × price per kWh. A 1,500 W appliance used for 3 hours at 0.25 EUR/kWh therefore costs 1,500 × 3 ÷ 1,000 × 0.25 = 1.125 EUR per use. Add quantity and frequency only for totals beyond one appliance and one use; actual cycling, measured consumption, fees, and changing tariffs can make the bill differ.

First calculate kWh

Energy per use = watts × hours ÷ 1000 × quantity. A 1500 W heater running for 3 hours uses 1500 × 3 ÷ 1000 = 4.5 kWh. If runtime is in minutes, divide minutes by 60 before applying the equation. Keep units beside each value so watts are not accidentally treated as kilowatts.

Then apply the rate and frequency

Cost per use = kWh per use × price per kWh. At 0.25 EUR/kWh, 4.5 kWh costs 1.125 EUR. One use per day for 30 days gives 135 kWh and 33.75 EUR. A 365-day projection is a comparison baseline, not a prediction that the same usage or tariff will persist.