How this calculator works
Electricity is billed in kilowatt-hours (kWh): the power in kilowatts times the hours it runs. A 2,000 watt heater is 2 kW, so one hour uses 2 kWh. Multiply by your price per kWh, in pence, and divide by 100 for pounds. Appliances that cycle (a thermostat heater, a fridge, an oven) do not draw full power all the time, so the calculator lets you enter the average share of the rating.
Worked example: a 2,000 W fan heater at full power for 4 hours a day uses 8 kWh a day, which costs £2.16 a day at 27p. Over 30 days that is 240 kWh and £64.80. If its thermostat cycles it on for half the time, the cost halves to £32.40 a month.
Typical appliances at 27p per kWh
Typical running watts: check the label on yours. Appliances that cycle will average less.
| Appliance | Typical watts | Cost per hour | Per month at 2 h a day |
|---|---|---|---|
| LED light bulb | 8 W | £0.00 | £0.13 |
| Broadband router | 10 W | £0.00 | £0.16 |
| Laptop | 50 W | £0.01 | £0.81 |
| 55-inch LED TV | 80 W | £0.02 | £1.30 |
| Games console | 150 W | £0.04 | £2.43 |
| Desktop computer | 200 W | £0.05 | £3.24 |
| Slow cooker | 200 W | £0.05 | £3.24 |
| Microwave oven | 900 W | £0.24 | £14.58 |
| Air fryer | 1,500 W | £0.41 | £24.30 |
| Hair dryer | 1,800 W | £0.49 | £29.16 |
| Fan heater | 2,000 W | £0.54 | £32.40 |
| Condenser tumble dryer | 2,500 W | £0.68 | £40.50 |
| Kettle | 3,000 W | £0.81 | £48.60 |
| Electric shower | 8,500 W | £2.29 | £137.70 |
Tips before you buy
- The watts on a label are the maximum. A fridge-freezer rated at 150 W uses much less on average, because the compressor cycles. A plug-in energy monitor shows the real figure.
- The big costs in most homes are heating, hot water, the tumble dryer, the oven and an electric car, not chargers and lights. Look at those first.
- Standby power is small per device, but adds up: 30 W left on all year is about 263 kWh, which is about £71 at 27p per kWh. A smart plug or a power strip with a switch can turn devices off at the wall.
- A heat pump turns one unit of electricity into around three units of heat, so heating with one costs much less than a plug-in electric heater.
- If you are on a time-of-use tariff, price the hours you actually run the appliance at the rate for those hours.
Tools & materials for this project
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Frequently asked questions
How much does it cost to run a fan heater?
A 2,000 W fan heater at full power costs about 54p an hour at 27p per kWh, so about £2.16 for four hours and £64.80 for a month of four-hour days. Thermostat cycling lowers it.
How do I calculate the cost of electricity for an appliance?
Divide the watts by 1,000 to get kilowatts, multiply by the hours it runs to get kWh, then multiply by your price per kWh in pence and divide by 100.
How many kWh does a 1,000 watt appliance use?
One kWh for every hour it runs at full power: 24 kWh in a day of continuous use.
How do I convert amps to watts?
Multiply the amps by the volts. UK mains is 230 V, so a 13 A plug can supply up to about 3,000 W and a 10 A appliance draws up to 2,300 W.
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