Many appliances use electricity even when they aren’t powered on. This property is known as standby power, which is used to perform functions that must operate continuously. Energy saving measures often include unplugging electrical devices to eliminate the cost of keeping them in standby mode. This strategy requires you to estimate the cost of standby power for each appliance since it may not be worthwhile to unplug a device when it is not in use.

A year is about 8,766 hours long, so a month has an average duration of about 730.5 hours. This means you can multiply an appliance’s standby power in watts by 0.73 to obtain the kilowatts of energy it consumes each month, assuming it is always plugged in. A typical cost of electricity in the United States is 10 cents per kilowatt-hour. You can therefore estimate the standby cost of an appliance in dollars by multiplying its standby power consumption in watts by 0.0731.