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kVA to Amps Calculator

Line current in amps for a kVA rating at a given voltage and phase.

How it is calculated

Apparent power in kVA is multiplied by 1000 to get volt-amperes and divided by the voltage. For a single-phase supply the formula is I = kVA × 1000 / V; for a three-phase supply it is I = kVA × 1000 / (√3 × V), with √3 ≈ 1.732. I is the line current in amperes and V is the voltage in volts: phase-to-neutral for single phase, line-to-line (for example 400 V) for three phase. Phase is single unless three-phase is chosen. The voltage must be above zero and the kVA cannot be negative. The result is rounded to two decimals. Power factor is not an input: kVA already includes it, so the answer is the total current the conductors carry, not only the part doing useful work.

Worked example

A 50 kVA three-phase transformer feeds a 400 V line-to-line supply. Convert to volt-amperes: 50 × 1000 = 50 000 VA. The denominator is √3 × 400 = 692.8. The current is 50 000 / 692.8 = 72.17 A on each phase conductor. If the same 50 kVA were treated as single phase at 400 V, the formula would give 50 000 / 400 = 125.00 A, so choosing the wrong phase setting changes the answer by a factor of 1.73.

Try this example →

Common mistakes

  • Leaving the phase on single for a three-phase machine. At 400 V the same 50 kVA gives 125.00 A instead of 72.17 A, so cables and breakers would be sized far too big.
  • Using the phase-to-neutral voltage (230 V) in the three-phase formula. The √3 already accounts for the phase relationship, so enter the line-to-line voltage, here 400 V.
  • Entering kW instead of kVA. A kW rating is real power; dividing by the power factor gives kVA, and a load at 0.8 power factor draws a quarter more current than the kW figure suggests.
  • Typing the power in VA or MVA. The field takes kVA, so 50 000 VA must be entered as 50 and 0.5 MVA as 500.
  • Treating the result as a breaker rating. It is the rated full-load current; breakers, cables and starting currents need extra margin and local code rules.

About this calculator

Apparent power in kVA converts to current using I = (kVA × 1000) / V for a single-phase circuit, or I = (kVA × 1000) / (√3 × V) for a balanced three-phase circuit, where V is the line voltage. Because kVA includes both real and reactive power, this current figure is the total the conductor actually carries, not just the power-producing portion.

Electricians and electrical engineers use this conversion to size breakers, cables, and transformers from a generator or transformer's kVA nameplate rating, and to check that a panel's rated current can support the connected load.

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Comments (1)

  • Editorial team

    The same transformer rating gives very different line currents depending on phase: 100 kVA at 400 V is 144.34 A three-phase but 250.00 A single-phase. The answer is the total current the conductors carry, power factor already included in the kVA figure. Use it as a starting point for a design, and let a qualified electrician apply the rules for cable and breaker sizes. Which supply voltages would you like to see in the examples?

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