Transformer KVA Calculator
Calculate the KVA (Kilovolt-Ampere) rating of a transformer for single-phase or three-phase systems using voltage and current values.
Fill in the fields above and click Calculate.
Formulas
Single-Phase Transformer:
KVA = (V × I) / 1000
Three-Phase Transformer:
KVA = (√3 × V × I) / 1000
Where:
- V = Voltage in Volts (line voltage for single-phase; line-to-line voltage for three-phase)
- I = Current in Amperes (line current)
- √3 = 1.7321 (square root of 3, the three-phase multiplier)
- KVA = Apparent power in Kilovolt-Amperes
Assumptions & References
- KVA represents apparent power — it does not account for power factor (PF). To find real power (kW), multiply KVA × PF.
- For three-phase systems, the formula assumes a balanced load across all three phases.
- Voltage entered should be the line-to-line (line) voltage for three-phase, not the phase voltage.
- Current entered should be the line current (not phase current) in both cases.
- The √3 factor (≈ 1.7321) arises from the geometric relationship between line and phase quantities in a balanced three-phase system.
- This calculator is applicable for both the primary and secondary sides of a transformer — use the voltage and current from whichever side is known.
- Reference: IEEE Std C57.12.00 — General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.
- Reference: NEC (NFPA 70) Article 450 — Transformers and Transformer Vaults.