Appliance Energy Cost Calculator: Watts to Dollars

How the calculation works

Electricity is billed in kilowatt-hours (kWh). An appliance’s power, in watts, times the hours it runs gives watt-hours; dividing by 1,000 gives kWh. Multiply by your price per kWh and you have the cost.

kWh per year       = watts × hours per day × days per year ÷ 1,000
Cost per year      = kWh per year × price per kWh
Average per month  = cost per year ÷ 12
Cost per day used  = cost per year ÷ days per year

Watts. Use the figure on the appliance’s label or nameplate, or a reading from a plug-in electricity meter. The calculator assumes the appliance draws that power the whole time it is “on.”

Days per year. This lets you price seasonal devices fairly. A space heater used only in winter, or a window air conditioner used in summer, should not be counted for 365 days.

Price. The default is $0.18 per kWh, based on EIA’s U.S. residential average of 18.31¢ per kWh for July 2026. DOE’s Energy Saver guide makes the same point: to estimate what an appliance costs to run, you need its wattage, your local utility rate and your yearly usage.

Worked example

The default is a 1,500-watt appliance, such as a plug-in space heater on its high setting, used 4 hours a day for 120 days a year.

1. Energy used: 720 kWh a year.
2. At $0.18 per kWh, the cost is about $130 a year.
3. Spread over 12 months, that averages $10.80 a month.
4. Each day you use it costs about $1.08.

A second example

A 500-watt appliance, for example a dehumidifier in a damp basement (check your own model’s label), runs 12 hours a day for 150 days a year at the same $0.18 per kWh.

• Energy used: 900 kWh a year
• Cost: about $162 a year
• Average per month: $13.50
• Cost per day of use: $1.08

A device with a third of the wattage ends up costing more over the year because it runs longer and on more days. Hours of use matter as much as watts.

What your result means

The yearly cost is what the appliance adds to your electric bills if you use it as entered. The cost per day of use is handy for judging habits: is it worth running a space heater all evening, or a second freezer all year?

Compare the yearly figure with your total use. EIA reports that the average U.S. residential customer bought about 10,791 kWh in 2022. If one device is a large slice of that, it is worth a closer look. For devices that draw power even when they look off, use the phantom load calculator. For lighting, the LED savings calculator compares old and new bulbs. And to check your whole monthly bill, including fixed charges and tiers, try the electric bill calculator.

Rates and local factors that change the answer

Your rate plan. Many utilities charge a flat rate, but some use tiers, where kWh above a monthly threshold cost more, or time-of-use rates, where prices change by hour. Under a tiered plan, an extra appliance is billed at your top tier. Under time-of-use, running it off-peak can cut its cost.

Delivery charges and taxes. The “energy rate” on your bill is not always the whole story. Divide your total bill, minus fixed monthly charges, by the kWh you used to get a truer price.

Heating with plug-in heaters. A space heater can make sense for warming one room while the rest of the house is set back. Heating a whole house with plug-in heaters is usually expensive, because electric resistance heat costs far more per unit of heat than most alternatives. Our guide on how to lower your energy bill and the home energy audit guide cover better long-term fixes.

Rebates and help. When you replace an old appliance, many utilities offer rebates on ENERGY STAR models. The ENERGY STAR rebate finder lists offers by ZIP code. If your electric bills are hard to keep up with, see our guide to help paying energy bills.

Common mistakes

• Using the maximum wattage for appliances that cycle on and off, like refrigerators and heaters.
• Counting a seasonal device for all 365 days.
• Using only the supply or generation rate instead of the all-in price per kWh.
• Mixing up watts and kilowatts; 1,500 watts is 1.5 kW.
• Forgetting standby power from devices that are plugged in all the time.

Limits of this calculator

The tool assumes a constant power draw while the appliance is on. It does not model cycling, different power settings, standby use when “off,” tiered or time-of-use rates, or fixed monthly charges. Real costs can differ. This is an educational estimate, not advice.