How to work out what an appliance costs to run
- Enter the appliance’s Power in watts. It’s on the label or in the manual; for kilowatts, multiply by 1,000.
- Enter how many Hours a day it runs and your Price per kWh from your electricity bill.
- Read the cost per month, with the cost per hour, per day and per year and the energy it uses in a year.
Watts, kilowatt-hours and the label
Watts measure how fast a device uses power. A kilowatt-hour (kWh) is the energy used by 1,000 watts running for one hour, and it’s the unit on your bill. A 100 W TV on for 10 hours uses 1 kWh, the same as a 2,000 W kettle running for 30 minutes.
The power rating is printed on a sticker or plate on the back or underneath, or in the manual. If it only lists volts and amps, multiply them for an upper limit: 230 V × 10 A is 2,300 W. The label gives the maximum, so fridges, heaters and ovens that cycle on and off use less over a day than the number suggests.
The calculator counts a month as 30.44 days, the average length of a month over a year, and a year as 365 days.
Typical power ranges
These are rough ranges to help when you can’t find the label. Models vary a lot, so use your own appliance’s figure whenever you can.
| Appliance | Typical power |
|---|---|
| LED light bulb | 5 to 15 W |
| Laptop | 30 to 100 W |
| Television | 50 to 200 W |
| Hair dryer | 1,000 to 2,000 W |
| Portable space heater | 750 to 3,000 W |
| Electric kettle | 1,200 to 3,000 W |
A 10 W LED bulb left on around the clock uses 0.24 kWh a day. At 0.17 per kWh that is 1.24 a month, or 14.89 over a year.