Electrical circuits are rated by amperage, or "amps," to determine the amount of power that the outlet is capable of supplying. The electrical circuits found in most common households are 15-amp circuits. When more than 15-amps is pulled from the circuit by one or a combination of devices, the breaker in your service panel will trip, turning off the circuit as a precautionary measure. To determine the number of amps any one device pulls, you must know the wattage of the device, and the device's voltage.
Determine the number of volts and watts required by each device to be added to the circuit. The watts and volts are listed on a sticker on the device, often on the rear, beside the power cable. If the volts and watts are not listed, refer to the device's owner's manual.
Divide the number of watts required by the volts to determine the needed amperage. For example, a 120-watt device, requiring 1,200 volts requires 10 amps.
Add the total number of amps required by each device together to determine the amperage needed to safely operate all devices on the same circuit.