How to estimate what an appliance costs to run: watts x hours x rate
You can estimate the electricity cost of any plug-in appliance from three numbers: its power draw, how long you use it, and your price per kilowatt-hour.
The formula
- Monthly kWh = watts / 1,000 x hours per day x 30
- Monthly cost = monthly kWh x price per kWh
Example
A 1,500 W appliance used 30 minutes a day: 1.5 kW x 0.5 h x 30 = 22.5 kWh, which is about $3.83 a month. Used 2 hours a day it is 90 kWh, about $15.30. Cost scales directly with hours of use.
Things to check
- Wattage is on the product label or manual. Real draw changes with the operating mode.
- Your utility may charge different rates by usage tier or time of day. Check your bill for the actual rate.
- Heating and cooling appliances draw the most, so hours matter most for them.
- For always-on appliances such as a refrigerator, use the labelled yearly kWh figure if there is one.
Using it to compare
For two similar products, multiply the wattage difference by your expected hours to get the yearly electricity difference, then weigh it against the price difference. See total cost of ownership for the full method.