Cost = watts ÷ 1,000 × hours used × price per kWh. A 3,000 W kettle used for 15 minutes a day uses 0.75 kWh per day, which costs about 20p at an example price of 26p per kWh. Your own price is on your bill or app, so swap it in.
What a kilowatt-hour is
Electricity is billed in kilowatt-hours (kWh). One kWh is one kilowatt (1,000 watts) used for one hour. So a 1,000 W heater running for an hour uses 1 kWh, and so does a 100 W bulb left on for ten hours.
The power of an appliance, in watts, is usually on a label on the back or underneath it, or in the manual. Heating appliances such as kettles, heaters and ovens use the most power while they are heating, but they may cycle on and off, so real use can be lower than the label suggests.
The formula
- Convert watts to kilowatts: watts ÷ 1,000.
- Multiply by hours used to get kWh.
- Multiply by your price per kWh to get the cost.
The price per kWh is your own tariff, which differs between suppliers and changes over time, so we do not quote a current rate. Examples here use 26p per kWh purely to show the method.
Worked example 1: a kettle
Take a 3,000 W kettle that is on for 15 minutes (0.25 hours) a day, every day, with the Electricity cost of appliances tool.
- Energy per day: 3 kW × 0.25 h = 0.75 kWh.
- Cost per use at 26p: about 20p.
- Energy per year: about 273.8 kWh.
- Cost per year: about £71.18, or £5.93 a month.
Worked example 2: a 100 W device left on
Suppose a 100 W device is used for 5 hours a day, every day.
- Energy per day: 0.1 kW × 5 h = 0.5 kWh.
- Energy per year: 182.5 kWh.
- Cost per year at 26p: about £47.45, or £3.95 a month.
A low-power device used for long hours can cost as much as a high-power one used briefly. That is why the hours matter as much as the watts.
Typical appliances to check
The calculator has presets for common items, including an LED bulb, television, laptop, gaming PC, kettle, microwave, electric oven, air fryer, washing machine, tumble dryer, dishwasher, heater, hair dryer, electric shower and EV home charger. These are typical figures only, so enter the watts from your own label if you can.
For a washing machine or dishwasher, the cost depends on the programme and temperature, so use the figure on the energy label or a plug-in meter if you want precision. For an electric car, the same method applies: kWh added to the battery × your price per kWh. The guide to Fuel cost and mpg: UK gallons, litres and trip costs covers the equivalent for petrol and diesel.
Ways to bring the cost down
- Switch off devices at the wall if they use standby power.
- Choose a lower-temperature wash and fuller loads.
- Only boil the water you need.
- Use a plug-in energy meter to find out what your real appliances use.
- Check whether your tariff has cheaper off-peak periods, and run big appliances then if it suits you.
If you want to know how much a change saves in percentage terms, see How to calculate percentages.
Note: These are estimates, and standing charges are not included. Check your tariff and bill for your real costs. This is general information, not advice.
Making sense of the result
A yearly figure can look larger than expected, so put it in context. Multiply by the share of the year you really use the appliance, and be honest about the hours. A tumble dryer used twice a week is very different from one used daily. Setting the days per week in the calculator handles this, and you can compare two appliances by running both through the same tool with the same price.
If you are thinking of replacing an old appliance, work out its running cost now, then the running cost of the new model from its energy label, and compare the saving over several years with the purchase price. That tells you whether an upgrade pays for itself.
Try the calculator
Pick an appliance in the Electricity cost of appliances tool, enter your own price per kWh and the hours you use it, and it shows the cost per use, per day, per month and per year.
Open the free Electricity cost of appliances
Frequently asked questions
How do I work out the cost of running an appliance?
Multiply its power in kilowatts by the hours used, then by your price per kWh.
What is a kWh?
A kilowatt-hour is the energy used by a 1,000 W appliance running for one hour. It is the unit your supplier bills you in.
Where can I find my price per kWh?
On your bill, your supplier’s app or your tariff documents. It varies by supplier and tariff.
Does the calculation include the standing charge?
No. The standing charge is a daily fee that you pay regardless of use, so it is separate from the cost of running an appliance.