How much does it cost to run?

How do I calculate the cost of running an appliance?

Multiply the watts by the hours it runs and divide by 1,000 to get kilowatt-hours, then multiply by your price per kWh. A 1,500 W space heater running 4 hours a day uses 1,500 × 4 ÷ 1,000 = 6 kWh a day. At 18.31¢ per kWh that is $1.10 a day, $33.42 a month and about $401 a year.

What is the average price of electricity in the US?

The U.S. Energy Information Administration reports an average of 18.31 cents per kWh for homes in July 2026. Prices differ a lot from state to state and between utilities, so for your own number divide the energy charges on your bill by the kWh you used.

How do I find how many watts an appliance uses?

Look for the label or nameplate on the back or bottom, or in the manual. If it lists only amps, multiply by the voltage: 10 A at 120 V is 1,200 W. A plug-in electricity usage meter shows the real draw, which is often below the nameplate maximum.

What is a kilowatt-hour?

One kilowatt-hour (kWh) is 1,000 watts used for one hour. A 100 W bulb left on for 10 hours uses 1 kWh, and so does a 1,000 W microwave running for an hour. Your utility bills you by the kWh.

Why is my bill higher than the calculator shows?

Bills add fixed customer and delivery charges and taxes on top of the energy itself. Also, fridges, freezers, air conditioners and heaters cycle on and off, so enter the hours they actually run rather than the hours they are plugged in — or measure them with a usage meter.

How do I handle an appliance that cycles on and off?

Enter the hours it actually runs, not the 24 it is plugged in. A refrigerator-style load of 700 W that runs 40% of the time is 9.6 hours a day: 6.72 kWh a day, about 204 kWh a month, or $37.43 a month at 18.31¢. A plug-in usage meter shows the real figure over a week.

How do I find watts from volts and amps?

For resistive loads such as heaters and incandescent bulbs, watts = volts × amps. For motors and electronics the true power can be lower than volts times amps because of the power factor, so a nameplate in amps tends to overstate the draw. Use the wattage on the label or measure it.

The formula and what it leaves out

Energy in kilowatt-hours = watts × hours ÷ 1,000, and the cost is the energy times your rate per kWh. For a month the calculator uses an average month of 365 ÷ 12 days. The rate is the energy charge only: it does not include the fixed monthly customer charge on your bill, demand charges for some commercial accounts, time-of-use pricing, or tiered rates that rise with use. For a rough estimate, divide your bill’s total by the kWh you used to get an all-in price per kWh and enter that instead.

Worked example: a desktop computer

Suppose a desktop draws 150 W for 8 hours a day. That is 150 × 8 ÷ 1,000 = 1.2 kWh a day, 36.5 kWh in an average month and 438 kWh a year. At 18.31 cents per kWh the cost is $0.22 a day, $6.68 a month and $80.20 a year. Twenty 9 W LED bulbs lit 5 hours a day use 329 kWh a year and cost $60.15, a reminder that many small loads add up.

Common mistakes

Confusing kW and kWh is the usual one: a kilowatt is a rate of use, a kilowatt-hour is an amount, and bills are in kWh. Using a nameplate maximum for a device that rarely runs at full power overstates the cost, while ignoring standby draw understates it for devices that are always plugged in. Entering minutes as hours (or the reverse) throws the result off by a factor of 60. Finally, check the rate: the national average is a starting point, and your own rate may be quite different.

Sources: U.S. Energy Information Administration, Electric Power Monthly (average residential price) and “Units and calculators explained” (kilowatt and kilowatt-hour). Related: EV charging calculator, heating cost calculator, battery runtime calculator and solar panel calculator.