What is kVA?
Also known as: Kilovolt-Ampere
kVA (kilovolt-ampere) is a unit of apparent power used to rate electrical equipment like UPSes and PDUs, equal to 1,000 volt-amperes, and differs from kilowatts when the power factor is not 1.0.
kVA stands for kilovolt-ampere, a unit of apparent power in an electrical circuit. Apparent power combines real power (measured in kilowatts, kW) and reactive power (measured in kilovolt-ampere reactive, kVAR). The relationship is kVA = kW / power factor. For a purely resistive load with a power factor of 1.0, kVA equals kW. For inductive or capacitive loads (common in IT equipment with switched-mode power supplies), the power factor is less than 1.0, so kVA is greater than kW.
In data centers, kVA ratings are critical for sizing uninterruptible power supplies (UPSes), power distribution units (PDUs), and generators. A UPS rated at 100 kVA can deliver 100 kVA of apparent power, but the actual usable real power depends on the load's power factor. Modern UPSes often have a rated output power factor (e.g., 0.9), meaning a 100 kVA UPS can deliver up to 90 kW of real power. Overloading a UPS beyond its kVA rating can cause overheating or failure, regardless of the kW draw.
kVA is also used for transformer ratings, circuit breaker sizing, and electrical service capacity. When planning data center power infrastructure, engineers must consider both kVA and kW to avoid undersizing conductors or overloading equipment. The ratio of kW to kVA (power factor) is a key metric for efficiency; a lower power factor increases kVA for the same kW, requiring larger cables and UPS capacity.
Key facts
- kVA = kW / power factor; at unity power factor (1.0), kVA equals kW.
- UPS and PDU capacity is typically rated in kVA, not kW.
- Modern data center UPSes often have a rated output power factor of 0.9.
- Reactive loads from switch-mode power supplies lower the power factor, increasing kVA relative to kW.
- Overloading a UPS beyond its kVA rating can cause thermal failure even if kW draw is within limits.
How it works in practice
Related terms
References
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