Appliance Energy Cost Calculator

1. Pick what you know: the watts, the EnergyGuide kWh per year, or the amps and volts from the nameplate.
2. Enter the hours used per day and the days used per year. Use fewer days for a heater or air conditioner that runs only part of the year.
3. For a fridge, AC or heater with a thermostat, add a duty cycle. For a device that stays plugged in, add its standby watts.
4. Type your price per kWh from your bill. The $0.17 default is only an example.
5. Read kWh and cost per day, per 30 days and per year. Press Add to list to total several appliances.

The working under the result shows each step, so you can check the math against your own notes.

Energy is power multiplied by time. A kilowatt-hour (kWh) is 1,000 watts running for one hour, which is why the watts are divided by 1,000.

W is the running watts, h the hours used per day, d the duty cycle as a decimal (100% = 1) and S the standby watts for the other hours.

N is the days used per year. Standby keeps running on the days the appliance is not used, as long as it stays plugged in.

P is your price per kWh, I is current in amps and PF is the power factor. Motors have a power factor below 1, so volts x amps gives an upper bound, not the real draw.

These rows are computed with the formulas above. The wattages and hours are typical examples only, so check the label on your own appliance.

A seasonal space heater can cost more than a fridge that runs all year. A small standby load still adds a few dollars because it never stops.

The wattage stamped on an appliance is the most it can draw. Many devices run at lower settings, so the real number is often smaller.

How to Measure

Plug an electricity usage monitor into the outlet, then plug the appliance into the monitor. It shows the watts right now. Leave it in place for a day or a week to read the kWh, which captures cycling and standby.

What It Cannot Measure

Plug-in monitors work on 120 V devices. Large 240 V appliances, such as dryers, central air conditioners and water heaters, need a circuit-level or whole-house monitor.

If you measured kWh over several days, divide by the days to get kWh per day. Then enter it with the label mode as kWh per day x 365.

A fridge, freezer, air conditioner or space heater with a thermostat does not run at full power the whole time it is on. The compressor or element switches on and off to hold the set temperature.

The duty cycle is the share of time it really runs. The U.S. Department of Energy suggests treating a refrigerator as running about one third of the time, which is a 33% duty cycle.

Hot days, a low thermostat setting or frequent door opening raise the duty cycle. A plug-in meter gives the best number: measured kWh / (watts x hours / 1,000) is your duty cycle.

Many devices draw a little power while switched off: TVs, game consoles, chargers, microwaves and computers. This is called standby power or a phantom load.

Berkeley Lab reports that most products now draw less than 0.5 W in standby. Because a home has so many of them, together they make up about 5 to 10% of home electricity use.

A 5 W standby load for all 8,760 hours of a year uses 43.8 kWh, or $7.45 at $0.17 per kWh. A switched power strip cuts it to zero.

The yellow EnergyGuide label appears on refrigerators, freezers, dishwashers, clothes washers, water heaters, room air conditioners, televisions and several other products.

It shows an estimated yearly energy use in kWh and an estimated yearly cost. The FTC notes that the cost is based on typical use and a national average price, so your own cost depends on your use and your local price.

For a better estimate, enter the kWh figure in label mode and your own price. A 600 kWh per year fridge costs $102.00 a year at $0.17 per kWh.

1. A 900 W window air conditioner runs 8 hours a day for 90 days of summer. The compressor cycles, so assume a 50% duty cycle.
2. Energy per day: 900 x 8 x 0.5 / 1,000 = 3.6 kWh.
3. Cost per day at $0.17: 3.6 x 0.17 = $0.61 (unrounded $0.612).
4. Per 30 days: 108 kWh, or $18.36.
5. Per season: 3.6 x 90 = 324 kWh, or $55.08.

Without the duty cycle the estimate would double to $110.16, so a realistic duty cycle matters.

Multiply the watts by the hours it runs per day and divide by 1,000 to get kWh per day. Then multiply by your price per kWh. A 1,500 W space heater run 4 hours a day uses 1,500 x 4 / 1,000 = 6 kWh. At $0.17 per kWh that is $1.02 a day, or $30.60 over 30 days.

The duty cycle is the share of time the compressor or heating element is actually on. Fridges, air conditioners and space heaters with a thermostat cycle on and off. The U.S. Department of Energy suggests counting a refrigerator as running about one third of the time. A 900 W window AC set for 8 hours at a 50% duty cycle uses 3.6 kWh a day, not 7.2 kWh.

A device that draws 5 W around the clock uses 5 x 8,760 hours / 1,000 = 43.8 kWh a year. At $0.17 per kWh that is $7.45 a year. Berkeley Lab reports that most products now draw less than 0.5 W in standby, but all the always-on devices in a home together add up to 5 to 10% of home electricity use.

Find the estimated kWh per year on the yellow EnergyGuide label and multiply it by your own price per kWh. A refrigerator rated at 600 kWh per year costs 600 x $0.17 = $102.00 a year. The dollar figure printed on the label uses typical use and a national average price, so your cost can differ.

Yes, as an upper bound. Watts = volts x amps x power factor, and the power factor of a motor is < 1, so volts x amps is at or above the real draw. Nameplate amps are also a maximum rating. Most U.S. appliances run on 120 V, and dryers and ranges on 240 V. A 4.5 A dehumidifier on 120 V is at most 540 W.

Usually not. The wattage on the nameplate is the maximum the appliance can draw, and many devices run at lower settings most of the time. A plug-in electricity usage monitor shows the real watts and the kWh over a day or a week. These monitors work on 120 V plug-in devices, not on 240 V appliances such as dryers or water heaters.

Use your own bill. Divide the total charges, including delivery and taxes, by the kWh you used that month. The $0.17 default is only an example. Residential prices vary a lot by state; the EIA Electric Power Monthly, Table 5.6.A lists average prices in cents per kWh for each state.

• U.S. Department of Energy, Energy Saver: Estimating Appliance and Home Electronic Energy Use (archived copy) (kWh per day = watts x hours / 1,000; nameplate wattage is the maximum; watts = amps x volts, 120 V or 240 V; refrigerators run about one third of the time; plug-in usage monitors for 120 V devices; phantom loads).
• Federal Trade Commission: How To Use the EnergyGuide Label To Shop for Home Appliances (which products carry the label; the cost estimate uses typical use and a national average price).
• Lawrence Berkeley National Laboratory: Standby Power (most products draw less than 0.5 W in standby; together standby is 5 to 10% of residential electricity use).
• U.S. Energy Information Administration: Electric Power Monthly, Table 5.6.A (average residential electricity price by state, in cents per kWh).