Electricity cost calculator
Find it on the label.
Use the price from your bill if you know it.
Cost to run this device
Cost = watts divided by 1,000, times hours, times your price per kWh. It covers energy only, not the cost of buying the device.
How the calculation works
Electricity is billed in kilowatt-hours. One kilowatt-hour is the energy a 1,000 watt device uses in one hour. The calculator does three steps:
- Convert watts to kilowatts by dividing by 1,000.
- Multiply the kilowatts by the hours of use to get kWh.
- Multiply the kWh by your price per kWh to get the cost.
You can find the watts on the label on the back or bottom of the device, in the manual, or with a plug-in watt meter. A label gives the maximum draw. Devices with a thermostat, such as a refrigerator or an air conditioner, cycle on and off, so their real average draw is lower than the label.
What common devices cost to run
These examples use round wattages to show the method. Your own devices will differ, so check the label before you rely on a number.
| Device | Watts | Hours a day | kWh a month | Cost a month |
|---|---|---|---|---|
| LED light bulb | 9 | 5 | 1.3 | $0.23 |
| Laptop computer | 60 | 8 | 14.4 | $2.48 |
| Window air conditioner | 1,000 | 8 | 240.0 | $41.36 |
| Space heater on high | 1,500 | 4 | 180.0 | $31.02 |
| Electric clothes dryer | 3,000 | 1 | 90.0 | $15.51 |
Source: Price: 17.23 cents per kWh, the 2025 US residential average from EIA Form EIA-861. Wattages are illustrative.
Which price per kWh should you use
The most accurate price is your own. Take the total on a recent bill and divide it by the kWh used. That gives an all-in price that includes delivery, fixed charges and taxes. If you do not have a bill handy, pick your state in the calculator to start from its 2025 average, or use the state electricity rate table.
One catch
What the result leaves out
- The monthly fixed charge on your bill, which you pay even if you use nothing.
- Standby power from devices that stay plugged in.
- Seasonal swings. A heater or air conditioner runs far more in some months than others.
- The cost of buying, installing or maintaining the device.
Frequently asked questions
How do I calculate what an appliance costs to run?
Divide the watts by 1,000, multiply by the hours it runs, and multiply by your price per kWh. For a 100 watt device that runs 10 hours, that is 1 kWh, which costs about 17 cents at the US average price.
How much does it cost to leave something on all day?
Multiply watts by 24 and divide by 1,000 to get kWh a day. A 100 watt device left on all day uses 2.4 kWh, which costs about $0.41 at the 2025 US average price.
Why does my result differ from my bill?
The calculator prices one device. Your bill adds every other device, a fixed monthly charge, taxes and sometimes tiered or time-of-use prices. Use the electric bill calculator for the whole bill.
Where do I find the wattage of my appliance?
Look for a label on the back, bottom or inside the door. It lists watts, or amps and volts. Multiply amps by volts to get watts. A plug-in watt meter measures real use for any device that plugs into an outlet.