Electricity Cost Calculator
Enter an appliance’s wattage, daily hours and your rate per kilowatt-hour. A 1,200 watt device running 2 hours a day at the example rate costs $10.80 per month.
How the electricity cost calculator works
Electricity is billed in kilowatt-hours (kWh). One kWh is one kilowatt, or 1,000 watts, used for one hour. To price an appliance, find its power in watts, estimate how many hours a day it runs, and multiply by the price your utility charges per kWh.
The wattage is usually printed on the label, the plug or the manual. Use the real running hours, not the hours the device is plugged in. A refrigerator, for example, is on all day but its compressor only runs part of the time, so its average draw is lower than its label rating.
The formulas
Example: A 1,200 watt appliance used 2 hours a day uses 2.4 kWh per day. At an example rate of $0.15 per kWh, that costs $0.36 per day, $10.80 per month and $131.40 per year. The monthly energy is 72 kWh. The rate here is an illustration, not a national average.
Finding your rate
Your rate is on your electric bill. Look for the price per kWh, or divide the energy charge by the kWh used. Some bills add delivery charges, fixed fees and taxes, so the true cost per kWh can be higher than the headline energy rate. Some utilities also charge different rates by time of day or by usage tier. The U.S. Energy Information Administration publishes how homes use electricity if you want to see where the biggest loads usually come from.
Limits
The tool assumes the appliance draws its rated power the whole time it runs. Devices with motors, thermostats or variable speed settings draw less than their maximum much of the time, and standby power is not counted. A plug-in power meter gives a measured figure. For sizing heating and cooling equipment, see the BTU calculator and the HVAC sizing calculator.
Reading the results
The calculator shows cost per day, month and year, plus the energy used per day and month. The yearly cost is the daily cost times 365, and the monthly cost uses a 30 day month. If an appliance only runs in certain seasons, such as a space heater or a window air conditioner, multiply the daily cost by the number of days it is actually used instead of using the yearly figure.
Common mistakes
The most common error is mixing up watts and kilowatts. A 1,500 watt heater is 1.5 kW, so one hour uses 1.5 kWh. The tool divides by 1,000 for you, so enter watts as printed on the label. If the label shows amps and volts instead, multiply them to get watts. For example, a device rated at 10 amps on a 120 volt circuit is rated at 1,200 watts.
Another mistake is using the wrong hours. A device used for 30 minutes a day should be entered as 0.5 hours. For several devices, run the calculator once for each and add the monthly costs. Comparing two models by their wattage and expected hours is a quick way to see whether a more efficient one pays back its higher price over time.
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Frequently asked questions
How do I calculate the cost of running an appliance?
Multiply watts by hours used, divide by 1,000 to get kWh, then multiply by your rate per kWh. The default example costs $0.36 per day.
Where do I find my rate per kWh?
On your electric bill. Use the all-in cost per kWh if you want delivery charges and fees included.
How much does it cost per month?
Multiply the daily cost by the number of days used. For the default inputs that is $10.80 for 30 days.
Why does my bill differ from this estimate?
Appliances rarely run at full rated power all the time, and bills include fixed charges, taxes and tiered or time-of-day pricing.
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