How to calculate the electricity cost of any device

You need three numbers: how much power the device draws (watts), how long it runs, and what you pay per kilowatt-hour (kWh). Multiply them and you have the cost. This guide walks through each step with a worked example at the latest U.S. average residential price of 18.16¢ per kWh (August 2026, EIA).

Step 1: find the power in watts

The rating is printed on a label on the device or its power adapter, or in the manual. If the label gives amps and volts instead, multiply them: watts = volts × amps. The rating is the maximum. Devices with a thermostat or compressor, such as refrigerators, heaters and air conditioners, switch on and off, so over a day they use less than the rating multiplied by the hours they are plugged in. For those, a plug-in energy meter or the yearly kWh figure on an efficiency label gives a better number.

Step 2: convert to kilowatt-hours

A kilowatt-hour is 1,000 watts used for one hour. Energy (kWh) = watts × hours per day × days ÷ 1,000. Example: a 1,500 W device used 2 hours a day for 30 days uses 1,500 × 2 × 30 ÷ 1,000 = 90 kWh.

Step 3: multiply by your price

Cost = kWh × price per kWh. At 18.16¢, those 90 kWh cost about $16.34 for the month. Where you live changes the answer a lot: at the highest state average, Hawaii (47.18¢), the same use costs $42.46; at the lowest, Nevada (12.72¢), it costs $11.45.

Which price to use

The most accurate price is your own. Take the total of your last bill and divide it by the kWh on that bill; the result includes fixed charges and taxes spread over your usage. State averages on this site are a good starting point when you do not have a bill, for comparing places, or for estimating a move. See how to read your electric bill.

Common mistakes

Mixing up watts and kilowatts (1 kW = 1,000 W); forgetting that cents need dividing by 100 to get dollars; using the plate rating for devices that cycle on and off; and ignoring standby power for devices that stay plugged in all day. The calculator handles the arithmetic once you have the inputs.