Home energy · kWh math
Appliance cost, from the label.
Enter the appliance's rated watts, how long it runs and the rate on your bill. For variable loads, use an average measured wattage.
Inputs
Estimated cost
Formula and caveats
Energy is watts × hours × days × quantity ÷ 1,000. Cost is kilowatt-hours × your rate. EIA explains the distinction: watts measure power at a moment, while watt-hours and kilowatt-hours measure energy over time.
The result is a planning estimate. Motors, compressors, heating elements and electronics may cycle, so a plug-in power meter is better than a nameplate for an appliance that does not draw its rated wattage continuously.
Source: U.S. Energy Information Administration — Measuring electricity