Power is measured in units called watts (W) . A watt is the unit of electrical power equal to one ampere under the pressure of one volt. One watt is a small amount of power, and some devices require only a few watts to operate, while others require larger amounts. The power consumption of small devices is usually measured in watts, and the power consumption of larger devices is measured in kilowatts (kW), or 1,000 watts. Electricity generation capacity is often measured in multiples of kilowatts, such as megawatts (MW) and gigawatts (GW) . The ratio of real power to apparent power is known as the power factor.