Enter the watts, the hours per day and the price per kWh. You get the cost to run the appliance per day, per month and per year.
How it is calculated
The method is the one Virginia Tech Extension uses for appliance energy: multiply the watts by the hours of use and divide by 1,000 to get kilowatt-hours, then multiply by the price of a kilowatt-hour. Annual energy is the daily energy times the number of days you use the appliance. The monthly figure is the yearly cost divided by 12, so a seasonal appliance is averaged over the whole year.
A refrigerator or freezer does not run all the time. The same publication says to count its hours as the plugged-in time divided by three, so the tool has a setting for appliances that cycle on and off.
Cost per day = kWh per day × price per kWh
Cost per year = kWh per day × days used per year × price per kWh
Cost per month = cost per year ÷ 12
Cycling appliances: hours = hours plugged in ÷ 3
The price box takes cents per kilowatt-hour. The starting value of 18.31 cents is the U.S. average residential price for July 2026 from the Energy Information Administration, up from 17.45 cents in July 2025. Your own price depends on your state and utility, so replace it with the number on your bill: divide the total charge by the kilowatt-hours used.
| Appliance | Typical watts | Cost per hour of use at 18.31 cents |
|---|---|---|
| Coffee maker | 900 to 1,200 | $0.16 to $0.22 |
| Clothes washer | 350 to 500 | $0.06 to $0.09 |
| Electric clothes dryer | 1,800 to 5,000 | $0.33 to $0.92 |
| Dishwasher | 1,200 to 2,400 | $0.22 to $0.44 |
| Dehumidifier | 785 | $0.14 |
| Hair dryer | 1,200 to 1,875 | $0.22 to $0.34 |
| Portable heater | 750 to 1,500 | $0.14 to $0.27 |
| Microwave | 750 to 1,100 | $0.14 to $0.20 |
| Ceiling fan | 65 to 175 | $0.01 to $0.03 |
| Window fan | 55 to 250 | $0.01 to $0.05 |
| Laptop | 50 | $0.01 |
| Television, 27 in. | 113 | $0.02 |
| Toaster | 800 to 1,400 | $0.15 to $0.26 |
| Vacuum cleaner | 1,000 to 1,440 | $0.18 to $0.26 |
| Water heater, 40 gal | 4,500 to 5,500 | $0.82 to $1.01 |
Worked examples
A desktop computer (120 W) and monitor (150 W), 4 hours a day, every day
Power: 120 + 150 = 270 W. Energy per day: 270 × 4 ÷ 1,000 = 1.08 kWh.
Energy per year: 1.08 × 365 = 394.2 kWh.
At 18.31 cents: 394.2 × 0.1831 = $72.18 a year, which is $6.01 a month and $0.20 per day of use. At the 8.5 cents used in that publication’s own example the same computer costs $33.51 a year.
A 725 W refrigerator plugged in around the clock
Cycling: 24 hours ÷ 3 = 8 hours of running time. Energy per day: 725 × 8 ÷ 1,000 = 5.8 kWh.
Energy per year: 5.8 × 365 = 2,117 kWh. At 18.31 cents that is $387.62 a year, or $32.30 a month.
A 1,500 W portable heater, 8 hours a day for 90 days
Energy per day: 1,500 × 8 ÷ 1,000 = 12 kWh, which costs 12 × 0.1831 = $2.20 per day of use.
Energy per year: 12 × 90 = 1,080 kWh, which is $197.75.
Finding the watts of your appliance
Look for a rating label on the back or bottom of the appliance, or in the manual. If the label gives only amps and volts, multiply them to get watts. Heating appliances such as heaters and toasters draw their full rated power whenever they are on. Motors, compressors and electronics often draw less than the label at times, so the label figure gives a safe upper estimate rather than an exact one.
What the result does not include
Your bill also has fixed charges, taxes and sometimes tiered or time-of-day prices, so the tool shows the cost of the energy itself. It is an estimate, not a replacement for a professional load calculation or a look at your own bill. For a whole-house picture, add up several appliances or use your meter data.
Frequently asked questions
How much does it cost to run a 100 watt device for 24 hours?
A 100 watt device uses 100 × 24 ÷ 1,000 = 2.4 kWh in a day. At 18.31 cents per kWh that costs about $0.44 per day, or roughly $160 a year if it runs all year.
What price per kWh should I use?
Use the number on your bill, found by dividing the total charge by the kWh used. As a starting point the tool uses the July 2026 U.S. average residential price of 18.31 cents. Prices differ a lot between states and utilities.
How do I enter a refrigerator or freezer?
Choose the setting for appliances that cycle on and off and enter 24 hours a day. The tool counts one third of the plugged-in time as running time, which is the rule extension specialists use for a refrigerator.
Why is the monthly cost the yearly cost divided by 12?
It averages seasonal use over the year. A fan used 120 days a year has a yearly cost that already reflects those days, so dividing by 12 gives a steady monthly figure.
Related calculators
Sources
Every figure on this page comes from the sources below. They were opened and checked while building the tool.
- Virginia Tech Extension (2020): BSE-301NP, Energy Series: Estimating Appliance and Home Electronic Energy Use
- Energy Information Administration (2026): Electric Power Monthly, Table 5.6.A, average price of electricity to ultimate customers (data for July 2026)