This electrical power calculator works with the relationship P equals V I, and solves it for the power, the voltage or the current. Electrical power is the rate at which a circuit uses or delivers energy, measured in watts, and it is simply the voltage across a device multiplied by the current flowing through it. You choose what to solve for, enter the other two values, and the calculator returns the answer in watts, volts or amps. To find power it multiplies voltage by current; to find voltage it divides power by current; and to find current it divides power by voltage. This last case is especially handy around the home, because appliances are usually rated in watts but circuits and fuses are rated in amps, so dividing the wattage by the mains voltage tells you the current an appliance draws. In New Zealand mains power is 230 volts at 50 hertz, so a 2300 watt heater pulls about 10 amps, close to the limit of a standard plug. Knowing the power also lets you work out running costs when combined with the time used and the price per kilowatt hour. This is essential for electronics, electrical work and understanding household energy use. Enter your two known values to see the result straight away.
The calculator uses P equals V I. To find power it multiplies voltage by current, to find voltage it divides power by current, and to find current it divides power by voltage. The quantity you are solving for is hidden so you only enter the two you know.
On New Zealand's 230 volt mains, a heater drawing 10 amps uses 230 times 10, which is 2300 watts. The same 2300 watt rating means it draws 2300 over 230, which is 10 amps.
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