How this calculator works
A single use is one running session: one oven cycle, one kettle boil, one washing machine load. The energy it takes is the power multiplied by how long the appliance is switched on, expressed in kilowatt-hours. The cost is that energy multiplied by the price per kilowatt-hour from the bill. Because the same relationship links power, time, energy and price, any one of them can be found when the others are known, which is useful when a nameplate rating is unclear or when you are checking whether a label claim is plausible.
Formula
energy in kWh = power in watts x time in hours / 1,000. cost = energy x price per kWh. power = energy / time. time = energy / power.
Worked example
A 2,000 W oven element running for one hour uses 2 kWh. At 15 cents per kWh that single use costs $0.30. Running the same element for 45 minutes uses 1,500 Wh / 1,000 = 1.5 kWh, and the same 2 kWh spread over 30 minutes implies a power of 4 kW.
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Frequently asked questions
What is the difference between this page and a monthly appliance cost?
This page prices one session. To build a monthly figure, multiply the cost of one use by the number of uses, or enter the total hours in the appliance wattage calculator.
Why is the label power sometimes much higher than the cost suggests?
Thermostatically controlled appliances cycle. An oven element rated 2,000 W does not draw that for the whole hour; the average draw is lower. Use the energy from a meter reading for the most accurate cost.
Should the tariff include delivery and taxes?
The energy charge is only one part of a bill. If you want the all-in cost of a use, enter a rate that already includes delivery, regulatory charges and taxes.
Does a 240 volt appliance need a different formula?
No. Watts already account for voltage and current. Volts times amps equals watts, so the kilowatt-hour arithmetic is unchanged.