KVA to Amps Calculator
KVA (kilovolt-amperes) is the standard rating for transformers, generators, and UPS systems. Electricians need to convert KVA to amps when sizing conductors, overcurrent protection, and disconnects for these devices. The conversion differs between single-phase and three-phase systems because three-phase power distributes the load across three conductors, effectively reducing the current per conductor.
Understanding the difference between KVA (apparent power) and KW (real power) is essential for commercial and industrial electrical work. Transformers are rated in KVA because they must supply current regardless of the load's power factor. A transformer rated at 75 KVA will supply 75 KVA whether the connected loads have a power factor of 0.8 or 1.0—but the real power delivered to the loads will be different.
This calculator handles both single-phase and three-phase conversions. Select the system type, enter the KVA rating and voltage, and the full-load amperage is calculated instantly. This is the amperage used for sizing feeder conductors per NEC Article 450 and selecting overcurrent protection devices.
KVA to Amps Formulas
Single-Phase: Amps = KVA × 1000 / Volts
Three-Phase: Amps = KVA × 1000 / (Volts × 1.732)
1.732 = √3 (square root of 3)
Common Transformer Amperage Reference
| KVA | 1Φ 240V | 3Φ 208V | 3Φ 480V |
|---|---|---|---|
| 15 KVA | 62.5 A | 41.6 A | 18.0 A |
| 25 KVA | 104.2 A | 69.4 A | 30.1 A |
| 37.5 KVA | 156.3 A | 104.1 A | 45.1 A |
| 50 KVA | 208.3 A | 138.8 A | 60.1 A |
| 75 KVA | 312.5 A | 208.2 A | 90.2 A |
| 100 KVA | 416.7 A | 277.6 A | 120.3 A |
| 150 KVA | 625.0 A | 416.4 A | 180.4 A |
| 225 KVA | 937.5 A | 624.7 A | 270.6 A |
How to Use This Calculator
- Enter the KVA rating — the apparent power rating of the transformer, generator, or load.
- Enter the voltage — defaults to 240V. Common values include 120V, 208V, 240V, 277V, and 480V.
- Select the phase — choose single-phase or three-phase to apply the correct formula.
- Read the result — the full-load amperage is calculated instantly.
Frequently Asked Questions
How do you convert KVA to amps?
For single-phase systems, divide KVA by voltage and multiply by 1,000: Amps = KVA × 1000 / Volts. For three-phase systems, divide by voltage times the square root of 3 (1.732): Amps = KVA × 1000 / (Volts × 1.732). For example, a 50 KVA single-phase transformer at 240V provides 208.3 amps.
What is the difference between KVA and KW?
KVA (kilovolt-amperes) is apparent power, while KW (kilowatts) is real power. The difference is the power factor. KVA = KW / Power Factor. Transformers and generators are rated in KVA because they must handle the total apparent power regardless of the load's power factor. For purely resistive loads (power factor = 1), KVA equals KW.
How many amps is a 75 KVA three-phase transformer at 208V?
A 75 KVA three-phase transformer at 208V provides approximately 208.2 amps. The calculation is: 75 × 1000 / (208 × 1.732) = 75,000 / 360.3 = 208.2 amps. This is the full-load amperage used for sizing conductors and overcurrent protection.