wikiHow Wattage Calculator Wattage is a measure of the rate at which energy is consumed or produced. To calculate wattage, you need to know the voltage and current of the circuit. The formula for calculating wattage is: Wattage = Voltage x Current This formula is known as Ohm's law. For example, if the voltage of a circuit is 120 volts and the current is 5 amps, the wattage can be calculated as follows: Wattage = 120 volts x 5 amps = 600 watts This means that the circuit is consuming or producing energy at a rate of 600 watts. It's important to note that wattage is not the same as the total amount of energy consumed or produced over time. To calculate the total energy consumed or produced over time, you would need to multiply the wattage by the amount of time. For example, if a 600-watt appliance is used for 3 hours, the total energy consumed would be: Total Energy = Wattage x Time Total Energy = 600 watts x 3 hours = 1,800 watt-hours. Page