What is volt-ampere (VA)? - Definition from WhatIs.com
Part of the Smart grid glossary:

Volt-ampere (VA) is a measurement of power in a direct current ( DC ) electrical circuit. The VA specification is also used in alternating current ( AC ) circuits, but it is less precise in this application, because it represents apparent power , which often differs from true power .

In a DC circuit, 1 VA is the equivalent of one watt (1 W). The power, P (in watts) in a DC circuit is equal to the product of the voltage V (in volt s) and the current I (in ampere s):

P = VI

In an AC circuit, power and VA mean the same thing only when there is no reactance . Reactance is introduced when a circuit contains an inductor or capacitor . Because most AC circuits contain reactance, the VA figure is greater than the actual dissipated or delivered power in watts. This can cause confusion in specifications for power supplies. For example, a supply might be rated at 600 VA. This does not mean it can deliver 600 watts, unless the equipment is reactance-free. In real life, the true wattage rating of a power supply is 1/2 to 2/3 of the VA rating.

When purchasing a power source such as an uninterruptible power supply ( UPS ) for use with electronic equipment (including computers, monitors, and other peripherals), be sure the VA specifications for the equipment are used when determining the minimum ratings for the power supply. The VA figure is nominally 1.67 times (167 percent of) the power consumption in watts. Alternatively, you can multiply the VA rating of the power supply by 0.6 (60 percent) to get a good idea of its power-delivering capability in watts.

Also see current , voltage , power , reactance , and watt .

This was last updated in March 2011
Contributor(s): Guillermo Cardenas
Posted by: Margaret Rouse

Related Terms


  • intranet of things

    - An intranet of things is, depending on your viewpoint, either an element of the all-encompassing Internet of Things (IoT) or an alternative model that uses similar systems and technologies but limi... (WhatIs.com)

  • smart home hub (home automation hub)

    - A smart home hub is a hardware device that connects the devices on a home automation network and controls communications among them. (WhatIs.com)

  • smart sensor

    - A smart sensor is a device that takes input from the physical environment and uses built-in compute resources to perform predefined functions upon detection of specific input and then process data ... (WhatIs.com)


  • Smart grid

    - Terms related to smart grids, including definitions about utility electricity delivery systems and words and phrases about smart meters and distributing, monitoring and billing electrical power.

  • Internet applications

    - This WhatIs.com glossary contains terms related to Internet applications, including definitions about Software as a Service (SaaS) delivery models and words and phrases about web sites, e-commerce ...

Ask a Question. Find an Answer.Powered by ITKnowledgeExchange.com

Ask An IT Question

Get answers from your peers on your most technical challenges

Ask Question

Tech TalkComment



    Contribute to the conversation

    All fields are required. Comments will appear at the bottom of the article.