Device energy cost calculator
Updated
Enter watts (or amps), hours of use and your electricity rate to see what any appliance or smart device costs per hour, month and year, standby power included.
Next steps
How the calculation works
The method is the one the Department of Energy uses: watts × hours used per day ÷ 1,000 = kilowatt-hours (kWh) per day, then kWh × your rate per kWh = cost. The calculator adds three refinements:
- Days per week, for devices you do not use daily.
- Time at full power, for devices that cycle: a space heater or air conditioner with a thermostat, or a freezer compressor, is not drawing full power every minute it is “on”.
- Standby power for the hours the device is plugged in but off, counted over the rest of the week (168 hours minus hours of use).
Example: a 1,500 W space heater running at full power 6 hours a day costs 1.5 kW × 6 h = 9 kWh a day. At 18¢ per kWh that is $1.62 a day, about $49 a month. If its thermostat keeps it at full power only 70% of the time, the cost drops to about $34 a month.
The default rate of 18¢ per kWh reflects the U.S. average residential price, which the EIA forecasts at about 18.2¢ for 2026. Rates vary widely by state and utility.
Common mistakes
- Using only the energy charge. Your real rate includes delivery charges and taxes. Divide the total of a recent bill (minus fixed monthly fees) by the kWh used to get it.
- Taking the label wattage as constant. The label shows the maximum. Heaters, air conditioners, refrigerators and dehumidifiers cycle, so set a realistic “time at full power”.
- Ignoring tiered or time-of-use rates. If your rate changes by time of day, run the calculation with the rate for the hours the device actually runs.
- Forgetting standby. Game consoles in instant-on mode, cable boxes and older chargers draw power all day. A plug-in power meter or an energy-monitoring smart plug shows the real figure.
Heating is usually the biggest line: see how a smart thermostat can trim it.
Frequently asked questions
Where do I find my device’s wattage?
On the rating label or nameplate, in the manual, or by plugging the device into a plug-in power meter or an energy-monitoring smart plug, which shows the actual draw.
How do I find my electricity rate?
Divide the total of a recent bill, minus fixed monthly charges, by the kWh used that month. That effective rate includes delivery and taxes, which the energy charge alone does not.
Why is my result different from my bill?
Most devices do not run at their label wattage all the time, and your bill includes everything else in the home plus fixed fees. Use the result to compare devices and habits, not to predict the full bill.