Amperes is the standard unit of measurement used to rate the capacity of circuits to carry electrical load. It determines how many items you can plug into your electrical circuits. You can compute the amperes of any electrical item. The formula for amperes is watts divided by volts. If you get all appliances or electrical items that would be plugged or connected to a circuit and add up all their amperes, the resulting figure would be the total load for that circuit. The total load of that circuit in amperes should not exceed 80 percent of the ampere rating of the circuit breaker.
Determine if the voltage of electrical item is 220 or 110 volts. You can check the manufacturer's tag located at the bottom or side of the item and look at the voltage.
Look at the manufacturer's tag again and check the wattage. A watt is the standard unit that is used to measure the rate electricity is converted into energy.
Divide watts by volts. For example, if you have 1,100 watts and the voltage is 110 volts, the result is 10 amperes.