How this calculator works
Electrical power in watts multiplied by hours gives watt-hours; dividing by 1000 converts that to kilowatt-hours, the unit on your bill. Multiplying by the price per kilowatt-hour gives the energy charge. The estimate assumes a constant average load for all the hours entered and one flat tariff, so a device that cycles on and off should use its average draw or its equivalent full-load hours rather than both the peak and the duty cycle.
Formula
energy_kwh = power_watts x hours_per_day x days / 1000. energy_cost = energy_kwh x price_per_kwh.
Worked example
A 1500 W appliance run 2.5 hours a day for 30 days uses 112.5 kWh. At $0.15 per kWh the energy charge is $16.88.
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Frequently asked questions
Why is my bill higher than this estimate?
The estimate covers the energy charge only. Fixed delivery charges, demand charges, tiered or time-of-use pricing and taxes are outside it unless you enter a rate that already includes them.
Should I use the label wattage?
The label figure is often a maximum. For a fair estimate use an average draw from a meter, or the typical duty cycle: a heater that runs half the time at 1500 W averages 750 W.
Does the formula change in the United States?
No. Kilowatt-hours and a price per kilowatt-hour work the same way; only the currency and tariff differ, so enter your local rate.