What your appliances really cost to run

7 minute read · updated 2026-10-19

Quick answer: Running cost = watts ÷ 1,000 × hours used × your price per kWh. A 2,000 W heater used for 3 hours at £0.25 per kWh costs 2 × 3 × 0.25 = £1.50.

Electricity is sold by the kilowatt-hour. Once that one unit makes sense, working out what anything in your house costs to run becomes simple arithmetic, and some of the answers are surprising.

What a kilowatt-hour is

A watt is a rate: how fast an appliance draws power while it is switched on. A kilowatt is a thousand watts. A kilowatt-hour, usually written kWh, is what you use when you run a kilowatt for an hour.

So a 1,000 watt appliance running for one hour uses one kWh. The same appliance running for half an hour uses half a kWh. A 2,000 watt appliance running for half an hour also uses one kWh. Power multiplied by time is all that is going on.

Your electricity meter counts kWh, and that is what you are billed for.

Finding your price per kWh

Look at your latest electricity bill or your supplier's app for a figure in pence per kWh. It will be labelled something like unit rate or unit price.

There is a second charge on the same bill: the standing charge, a fixed daily amount you pay whether you use any electricity or not. Keep the two apart. The standing charge does not change when you boil the kettle, so leave it out when you are comparing appliances. It belongs in the question of what your bill totals, not what a device costs to run.

If you are on a tariff with different rates at different times of day, note each rate and when it applies. The same tumble dryer load can cost very different amounts depending on when you put it on.

The sum

Cost equals watts, divided by 1,000, multiplied by hours, multiplied by your price per kWh.

The examples below use 30p per kWh as an example price only. Prices vary enormously by country, supplier and tariff, and they change. Put your own rate in before you believe any of these numbers.

Kettle, 3,000 W, boiling for 3 minutes. 3,000 / 1,000 = 3 kW. Three minutes is 0.05 hours. 3 x 0.05 = 0.15 kWh. At the example price, about 4.5p a boil. Ten boils a day is 45p, or roughly £165 over a year.
Tumble dryer, 2,500 W, 90 minute cycle. 2.5 x 1.5 = 3.75 kWh, about £1.13 a load at the example price. Four loads a week is near £230 a year.
LED television, 100 W, four hours an evening. 0.1 x 4 = 0.4 kWh, about 12p, or roughly £44 a year.
Games console, 180 W, two hours a day. 0.36 kWh, about 11p a day.

Heat is what costs money

The pattern in those numbers is worth stating plainly. Anything whose job is to make heat uses a great deal of electricity. Anything whose job is to process information uses very little.

Kettles, toasters, tumble dryers, ovens, hobs, immersion heaters, electric showers, hair dryers, electric heaters: these are all rated in thousands of watts because heating water, air or metal takes real energy. An electric shower at 9,000 W uses 1.5 kWh in a ten minute shower, which is ten times a whole evening of television.

Laptops, phone chargers, routers, lights and televisions are rated in tens of watts. You can leave a phone charger plugged in all year and it will cost you pennies.

One wrinkle with thermostats. An oven rated at 2,100 W does not draw 2,100 W continuously. It heats up at full power, then cycles on and off to hold the temperature, so over an hour it might average half its rating. Fridges, freezers and heaters work the same way. For anything thermostatic, the sticker rating overstates the running cost, and the yearly kWh figure on the energy label is the better guide.

Standby

Standby power is real, but it is usually small. A device sitting idle might draw 0.5 W to 3 W. Take 2 W: over a full year that is 2 / 1,000 x 8,760 hours, which is 17.5 kWh, or about £5.25 at the example price.

Multiply that across a dozen devices and standby becomes a modest but genuine line on the bill, perhaps £30 to £60 a year in a well-stocked house. Worth switching off at the socket where it is easy, not worth losing sleep over. The exceptions are older set-top boxes and some games consoles, which can idle at 10 W or 15 W and cost real money.

Comparing two appliances fairly

To compare, you have to compare the same thing: energy used per job done, not power while running.

A 2,000 W machine that finishes in 20 minutes uses 0.67 kWh. A 1,000 W machine that takes an hour uses 1 kWh. The higher powered one is cheaper per job. Headline wattage on its own tells you nothing.

For big appliances, use the annual kWh figure on the energy label rather than the wattage, because it already accounts for cycles and thermostats. Then adjust for how you actually live. A label assumes a standard number of washes a year, and if you do twice as many, double it.

Tantoo has energy tools for a single appliance, a head-to-head comparison, whole home totals, showers and water, standby and time-of-use tariffs. You enter your own price per kWh, nothing is stored anywhere but your own device, and there is no account to make.