energy

How to calculate what an appliance costs to run

If a heater is rated at 2,000 watts and runs for two hours, it does not cost the same as a 2,000-watt heater used for 20 minutes. The two inputs you need are the appliance’s power rating and the time it actually runs.

The calculation

Use this sequence:

1. Divide watts by 1,000 to convert the rating to kilowatts.
2. Multiply kilowatts by hours used to get kilowatt-hours (kWh).
3. Multiply kWh by the electricity unit rate.

For example, a 1,000 W appliance used for 2.5 hours a day at £0.30 per kWh:

1,000 W / 1,000 = 1 kW
1 kW x 2.5 hours = 2.5 kWh per day
2.5 kWh x £0.30 = £0.75 per day
£0.75 x 30 days = £22.50 for that 30-day example

The result describes the stated use at the stated rate. It does not predict the whole electricity bill.

Use the label carefully

The number on an appliance label may be a maximum or nominal rating. A fridge, heater with a thermostat, or washing machine may not draw that power for the whole time it is switched on. If the appliance cycles, use a plug-in meter or other measured data when you can.

Write these beside the calculation:

• the wattage and whether it is a maximum or nominal figure;
• hours per day or the actual number of days used;
• the unit rate, currency, and date;
• the period you are calculating.

If the appliance is used on 12 days in a month rather than every day, the same example becomes 1 kW x 2.5 hours x 12 x £0.30 = £9.00.

Compare a few scenarios

These examples assume the stated rating for the full time shown and a unit rate of £0.30 per kWh:

Change the unit rate or the number of days when your situation differs. Keep the original inputs so you can replace the estimate with a reading later.

Keep the standing charge out of the appliance figure

The unit rate covers energy used in kWh. The standing charge is a separate daily charge for the supply, so adding the whole charge to each appliance would count it repeatedly. For the wider bill, check the unit rate, standing charge, meter readings, and whether the readings are actual or estimated in the guide to fixed and variable energy charges.

The estimate here covers the appliance’s usage. It does not include maintenance, replacement, or other ownership costs. For a heating system, keep fuel, system efficiency, and the heating period as separate inputs in the home-heating guide.

Before you use the number

Check the rating and likely running time, then decide whether one scenario is enough. If the hours are uncertain, calculate a low and high case. If you are buying or renting a home, confirm whether the appliance stays with the property. Finally, add the dated result to your annual home-cost budget.