kVA Calculator
Enter any two of voltage, current and apparent power (kVA) for single-phase or three-phase AC systems. The calculator solves for the missing quantity instantly.
How It Works
The kVA formula
Apparent power in kVA is the product of voltage and current, scaled by a phase factor:
Single-phase: kVA = V × I / 1000
Three-phase: kVA = √3 × V × I / 1000
Rearranging for the other quantities:
Current (A) = kVA × 1000 / (k × V)
Voltage (V) = kVA × 1000 / (k × I)
where k = 1 (single-phase) or √3 ≈ 1.7321 (three-phase)
Worked example
Single-phase: A 240 V, 50 A load has an apparent power of:
kVA = 240 × 50 / 1000 = 12 kVA
Three-phase: A 400 V, 100 A three-phase load:
kVA = √3 × 400 × 100 / 1000 ≈ 69.28 kVA
kVA Reference Table
Common single-phase apparent powers at 120 V and 240 V.
| Current (A) | 120 V (kVA) | 240 V (kVA) |
|---|---|---|
| 15 | 1.8 | 3.6 |
| 20 | 2.4 | 4.8 |
| 30 | 3.6 | 7.2 |
| 50 | 6.0 | 12.0 |
| 100 | 12.0 | 24.0 |
Frequently Asked Questions
What is kVA and how is it different from kW?
kVA (kilovolt-amperes) is apparent power: the total power drawn from the supply regardless of power factor. kW is real power, the portion that does useful work. The two are related by power factor: kW = kVA × power factor. For a purely resistive load the two are equal; inductive or capacitive loads reduce the power factor below 1, making kVA larger than kW.
How do I convert kVA to amps?
Rearrange the kVA formula: for single-phase, amps = kVA × 1000 / voltage. For three-phase, amps = kVA × 1000 / (√3 × voltage). For example, a 10 kVA single-phase load at 240 V draws 10,000 / 240 = 41.7 A.
Why is three-phase kVA calculated differently from single-phase?
A three-phase system delivers power on three conductors, each 120 degrees apart in phase. When you measure line-to-line voltage and line current, the total apparent power is √3 (approximately 1.732) times greater than the single-phase product V × I. This factor accounts for the combined effect of all three phases.
How do I size a transformer using kVA?
A transformer is rated in kVA (not kW) because it must handle the full apparent power regardless of power factor. Total up the kVA of all connected loads and add a safety margin of typically 20 to 25 percent to allow for future expansion and inrush current. Choose the next standard transformer size above your total. Use the transformer sizing calculator to find the primary and secondary full-load amps.
What is the difference between single-phase and three-phase kVA in practice?
For the same voltage and current, a three-phase system delivers √3 times more apparent power than single-phase. That is why large industrial loads (motors, welders, large HVAC) are always three-phase; you get roughly 73 percent more power without increasing conductor size. Single-phase is used where loads are smaller or where only two wires reach the equipment.
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