Apparent power is the product of RMS voltage and RMS current for a single-phase AC load. It is expressed in volt-amperes (VA); 1,000 VA equals 1 kVA.
VA and watts
Real power in watts describes the average rate at which electrical energy is transferred to the load. Apparent power includes the voltage-current demand associated with the complete waveform. Their ratio is power factor: PF = W ÷ VA.
Practical example
An illustrative load drawing 4 A RMS from 230 V RMS has an apparent power of 920 VA. At a power factor of 0.90, its real power is 828 W. Calling both figures “watts” would obscure the difference.
Reading supply ratings
Generators, inverters and backup supplies can have separate VA and watt limits, as well as transient or startup limitations. Both relevant continuous ratings and the permitted operating conditions matter. These single-phase relationships should not be substituted for the appropriate calculations and measurements on a three-phase distribution system.
Related terms
Power Factor · Watt · Voltage · Amperage · Inrush Current