kVA to Amps Calculator (Three-Phase and Single-Phase)
Convert transformer or generator kVA to full load current, or convert measured current back to kVA. Works for three-phase and single-phase at any voltage. The conversion needs no power factor — apparent power is voltage times current regardless of phase angle.
This is full load current, not a breaker size. Transformer overcurrent protection follows NEC Article 450 and feeder sizing follows Article 240; both apply their own multipliers and round to standard device ratings.
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The kVA to amps formula, and where the √3 comes from
Apparent power (kVA) is the product of voltage and current before power factor is considered. That makes the conversion to current purely geometric — you need the voltage and the phase configuration, nothing else.
On a single-phase circuit the relationship is direct: I = (kVA × 1000) ÷ V. On three-phase, the three line voltages are 120 degrees apart, so the line current relates to the line-to-line voltage through √3 (about 1.732): I = (kVA × 1000) ÷ (√3 × V).
Worked examples
- 75 kVA at 480 V, three-phase: (75 × 1000) ÷ (1.732 × 480) = 90.2 A
- 112.5 kVA at 208 V, three-phase: (112.5 × 1000) ÷ (1.732 × 208) = 312.3 A
- 25 kVA at 240 V, single-phase: (25 × 1000) ÷ 240 = 104.2 A
Note that the 112.5 kVA unit at 208 V draws far more current than the larger 75 kVA unit at 480 V. Current scales inversely with voltage, which is the entire reason distribution runs at higher voltages — the same power moves through a much smaller conductor.
kVA to amps: frequently asked questions
How do you convert kVA to amps on a three-phase system?
I = (kVA × 1000) / (√3 × V_LL). The √3 factor (about 1.732) comes from the 120-degree phase relationship between the three line voltages. For a 75 kVA transformer on a 480 V line-to-line system: (75 × 1000) / (1.732 × 480) = 90.2 A.
How do you convert kVA to amps on a single-phase system?
I = (kVA × 1000) / V. There is no √3 factor on single-phase. A 25 kVA single-phase transformer on 240 V draws (25 × 1000) / 240 = 104.2 A.
Does kVA to amps depend on power factor?
No. kVA is apparent power, which is the product of voltage and current regardless of phase angle, so the conversion needs only voltage and phase configuration. Power factor is required only when converting to or from kW (real power), because kW = kVA × pf.
Which voltage do I use, line-to-line or line-to-neutral?
Use line-to-line voltage with the √3 formula. On a 480Y/277 V system, 480 V is line-to-line and 277 V is line-to-neutral. Mixing them up is the most common source of an answer that is off by a factor of 1.732.
Is the calculated current the same as the breaker size?
No. The calculated value is full load current. Overcurrent protection and conductor sizing follow NEC Article 450 for transformers and Article 240 for feeders, which apply their own multipliers and round to standard device ratings. Size the protection from the code, not from this number alone.
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