Enter an appliance's power in watts and how many hours it runs, and this converts it to kilowatt-hours (kWh), the unit your bill is measured in. The cost is worked out at the current price cap, which you can change.
A kilowatt-hour is one kilowatt (1,000 watts) used for one hour. A 100W bulb left on for 10 hours uses 100 ÷ 1000 × 10 = 1 kWh. Your supplier bills per kWh (often called a "unit"), so converting to kWh is the step that turns a wattage into money. An appliance's wattage is usually on a label on the back or base, or in the manual.
Once you have the kWh, see kWh to cost, or skip straight to cost per use with the appliance running cost calculator. For where the big users hide, see electricity in the home.
Common questions
How do I convert watts to kWh?
Divide the watts by 1,000 to get kilowatts, then multiply by the hours it runs. A 2,000W heater for 3 hours is 2,000 divided by 1,000, times 3, which is 6 kWh.
How many kWh does a 1000W appliance use?
A 1,000W (1kW) appliance uses exactly 1 kWh for every hour it runs. Over 5 hours that is 5 kWh, which at 26.11p per kWh costs about £1.31.
Is a kWh the same as a unit on my bill?
Yes. One unit of electricity on a UK bill is one kilowatt-hour.