Electrical power is the rate at which electrical energy is consumed and is measured in Watts (W). One Watt is the amount of Joules (electrical energy) consumed per second. Electrical power can be calculated by multiplying the voltage and current measurement.

P = V x I

The following equations can also be used to calculate the power:

P = I^{2} x R

P = V^{2} / R

The polarity of the device has an affect on the measured power. If the current enters the device through the positive terminal of the device, a positive power measurement will be attained. Whereas if the current enters the device through the negative terminal of the device, a negative power measurement will be attained.

Due to the law of the conservation of energy, the amount power that is dissipated must be equal to the amount of power that is supplied.

The electrical power consumed by houses and industries is typically given in kilowatt hours, which is the amount of power consumed, given in kilowatts, multiplied by the time in hours.