Watts

• A watt is the unit used to measure the amount of actual flowing electrical energy.
  
  

Volts

• A volt is the unit used to measure the energy available in the electrical current of a circuit. Voltage controls the available electrical power (wattage).
  
  

Amperes

• An amp is the unit used to measure electrical current as it flows past a specified point.
  
  

Volt-Amps

• A volt-amp is the unit used to measure the apparent electrical power used by computing equipment. Mathematically, it is expressed as volts times amps (V*A).
  
  

Uses of Volt-Amp Measurements

• Because it represents the amount of energy computing systems may draw from a power grid, the VA is used to determine the kind of wiring and circuit breakers required to support the computing equipment in question.