VA stands for Volt-Ampere, which is a unit of measurement for electrical power in both direct current (DC) and alternating current (AC) circuits. In DC circuits, VA and watts (W) are equal, but in AC circuits, VA represents apparent power, which often differs from true power represented in watts. The difference between VA and watts is due to the presence of inductive resistance in AC circuits, which causes the voltage and current to be out of phase.

For determining power, watts are appropriate, but for determining capacity for the driving circuits, such as circuit breakers, wiring, and uninterruptible power supplies, VA is appropriate. When purchasing devices for use with electronic equipment, including computers, monitors, and other peripherals, its important to ensure that the volt-ampere specification is used when determining the power supplys minimum ratings.

In the context of inverters, VA refers to Volts x Amps, which is the electrical formula that gives you Watts. The VA measure has only an indirect relation to the efficiency and is a property specific to AC power setups. The value of VA is always greater than or equal to the value of watts, and the relationship between them depends on the power factor of the AC load.

In summary, VA is a unit of measurement for electrical power that represents apparent power in AC circuits and is appropriate for determining capacity for driving circuits. In the context of inverters, VA refers to Volts x Amps and is related to watts through the power factor of the AC load.