How to Calculate Appliance Electricity Running Cost in the UK

You only need three pieces of information for a basic running-cost estimate: the appliance power in watts, how long it runs, and your electricity unit price in pence per kWh.

The electricity cost formula

Electricity is billed in kilowatt-hours (kWh). Divide watts by 1,000 to get kilowatts, then multiply by hours used. Finally, multiply by the unit rate in pounds per kWh.

Cost in pounds = (watts ÷ 1,000) × hours × (pence per kWh ÷ 100).

Worked example: 2 kW electric heater

Imagine a 2,000-watt heater used for three hours, with an example tariff of 30p/kWh. This rate is for illustration, not a claim about current UK prices.

1. Power: 2,000 ÷ 1,000 = 2 kW.
2. Energy for three hours: 2 × 3 = 6 kWh.
3. Cost: 6 × £0.30 = £1.80 per session.
4. Used three times a week: £1.80 × 3 = £5.40 per week.
5. Over 52 weeks at the same usage: £5.40 × 52 = £280.80 per year.

Why actual bills can differ

An appliance's rated wattage is not always its average draw. Thermostats may cycle heaters on and off; washing appliances, fridges and air fryers have varying power use through a programme. If you know the proportion of time at full power, you can use an approximate load factor. Otherwise, a plug-in energy meter or an appliance's stated kWh per cycle often provides a better starting point.

This calculation estimates the energy unit charge only. Your household electricity bill may also include a daily standing charge and other tariff arrangements. Look at your own bill to find the unit price that applies to you.

Quick checks before comparing appliances

• Compare the same task, such as drying the same load of washing.
• Account for run time, not just wattage.
• For timed or programme-based appliances, use measured kWh if available.
• Review your tariff if the price or contract changes.

For the latest official explanation of tariffs and the energy price cap, see Ofgem's energy price cap guidance.

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