Many of the electronic devices in your home come with AC adapters. These adapters are designed to let devices like laptop computers and even video game consoles run on house current. If you want to calculate the total amount of power (called "wattage") that an AC adapter uses, you can do so using information present on the informational label on the adapter itself.
Look at the identification label on the side of your AC adapter. Write down the total number of volts and the total amperage the AC adapter uses. If these numbers are not listed on the side of the AC adapter, they will be listed in the manual that came with the device that uses the AC adapter. For example, if the AC adapter came with a laptop, the laptop's manual will have this information.
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Enter the number of volts into a calculator and select the "X" or "Multiplication" icon.
Enter the total number of amps into the calculator and press "Equals" or "Solve." The number on the screen is the total wattage that the AC adapter uses when powered on.