Do the math
How much does it cost to run an appliance?
The Simple Answer
Multiply the watts by the hours it runs, divide by 1,000 to get kilowatt-hours, and multiply by what you pay per kilowatt-hour. A 1,500-watt space heater running for 8 hours uses 12 kilowatt-hours, which is $1.92 at 16 cents.
Your bill charges for kilowatt-hours, which is a way of saying how much power you used and for how long. Once you know the watts on the label, the rest is multiplication.
The U.S. Energy Information Administration gives a tiny example: a 40-watt bulb used for five hours uses 200 watt-hours, which is 0.2 kilowatt-hours.
| Appliance | Watts × hours | Kilowatt-hours | Cost |
|---|---|---|---|
| 40-watt bulb | 40 × 5 | 0.2 | 3.2 cents |
| 100-watt television | 100 × 4 | 0.4 | 6.4 cents |
| 1,500-watt space heater | 1,500 × 8 | 12 | $1.92 |
The space heater for a month
8 hours a day: 12 kilowatt-hours × $0.16 = $1.92 a day
30 days: $1.92 × 30 = $57.60
That is the most it could cost. A heater with a thermostat usually switches itself off for part of the time, so the real figure is lower.
Where to find the numbers
- Watts: on the label or the plate on the back or bottom of the appliance, or in the manual. Some list amps and volts instead; multiply them to get watts.
- Hours: how long you really use it in a day. Be honest.
- Price: the rate per kilowatt-hour on your own electricity bill. It varies by place and changes over time, which is why the examples above use a made-up figure.
Things people often miss
Anything that makes heat, such as heaters, kettles, hair dryers and ovens, draws a lot of watts, so a short time still adds up. Anything that runs all day, such as a fridge, has a small wattage but a huge number of hours. Many devices also draw a little power while they are switched off but plugged in.