Power is a rate; energy is an amount
Watts (W) describe power at a particular moment. Divide watts by 1,000 to get kilowatts (kW). Kilowatt-hours (kWh) describe energy used over time. A device drawing 500 W steadily for two hours uses 0.5 kW × 2 h = 1 kWh. The same energy could power a 100 W device for ten hours.
Turn minutes into hours
For an illustrative 2,000 W kettle used for six minutes, enter 2 kW and 0.1 hours. The result is 0.2 kWh. Do not enter six hours or multiply kilowatts by minutes directly. Count how many times the appliance runs on an ordinary day, then include only the days it is actually used.
Choose the right measurement
A rating plate may show maximum power rather than normal consumption. A fridge cycles its compressor, while a washing machine changes power throughout a programme. Use measured kWh for a representative period or the energy figure for the relevant cycle. Check whether a label reports consumption per year, per cycle or per 100 cycles.
Separate consumption from the tariff
Multiply kWh by your applicable electricity price per kWh. Use the currency unit requested by the calculator and include applicable variable charges only once. Fixed account charges belong in a whole-bill estimate. They generally do not change when a single appliance runs for a shorter time.
Make the annual estimate realistic
A daily average multiplied by 365 is a planning scenario, not a meter reading. Holidays, seasonal cooling or heating, and changes in household size can alter it. Keep the input values alongside the result, then compare the estimate with measured consumption and revise the assumptions when they differ.
Data sources
- Ofgem · July–September 2026
- Ofgem: Understanding electricity and gas bills
- Ofgem: Price cap and standing charges explained
- Utility Regulator: Consumer information for Northern Ireland
Last reviewed: 2026-09-08