This kVA calculator converts between apparent power (kVA), current (amps) and real power (kW) for single-phase and three-phase systems. It is useful for sizing generators, transformers, UPS systems, cables and breakers.
kVA formulas
| Conversion | Single-phase | Three-phase |
|---|---|---|
| kVA → Amps | I = kVA × 1000 ÷ V | I = kVA × 1000 ÷ (√3 × V) |
| Amps → kVA | kVA = V × I ÷ 1000 | kVA = √3 × V × I ÷ 1000 |
| kW → kVA | kVA = kW ÷ PF | kVA = kW ÷ PF |
For three-phase systems, V is the line-to-line voltage (for example 208 V or 480 V in the US, 400 V or 415 V internationally, or 11 kV on medium-voltage systems). √3 is approximately 1.732.
kVA vs kW: the role of power factor
kW is the real power that does useful work. kVA is the apparent power the supply must deliver, including the reactive power (kVAR) that magnetises motors and transformers. They are linked by the power factor (PF): kW = kVA × PF. Generators and transformers are rated in kVA because their heating depends on current, not on how much of it does useful work. Most generators are rated at a power factor of 0.8, so a 100 kVA generator supplies 80 kW.
Worked examples
- 75 kVA at 208 V three-phase (208Y/120): I = 75,000 ÷ (1.732 × 208) = 208.2 A.
- 75 kVA at 480 V three-phase (480Y/277): I = 75,000 ÷ (1.732 × 480) = 90.2 A.
- 25 kVA at 240 V single-phase (120/240 V): I = 25,000 ÷ 240 = 104.2 A.
- 100 kVA at 400 V three-phase: I = 100,000 ÷ (1.732 × 400) = 144.3 A.
- 100 kVA at 480 V three-phase: I = 100,000 ÷ (1.732 × 480) = 120.3 A.
- 10 kVA at 240 V single-phase: I = 10,000 ÷ 240 = 41.7 A.
- 80 kW at 0.8 power factor: kVA = 80 ÷ 0.8 = 100 kVA.
kVA to amps quick reference (single-phase)
| kVA | 120 V | 230 V | 240 V |
|---|---|---|---|
| 1 | 8.3 A | 4.3 A | 4.2 A |
| 3 | 25 A | 13 A | 12.5 A |
| 5 | 41.7 A | 21.7 A | 20.8 A |
| 10 | 83.3 A | 43.5 A | 41.7 A |
| 15 | 125 A | 65.2 A | 62.5 A |
| 25 | 208.3 A | 108.7 A | 104.2 A |
| 37.5 | 312.5 A | 163 A | 156.3 A |
| 50 | 416.7 A | 217.4 A | 208.3 A |
| 75 | 625 A | 326.1 A | 312.5 A |
| 100 | 833.3 A | 434.8 A | 416.7 A |
| 167 | 1391.7 A | 726.1 A | 695.8 A |
kVA to amps quick reference (three-phase)
| kVA | 208 V | 400 V | 415 V | 480 V |
|---|---|---|---|---|
| 15 | 42 A | 22 A | 21 A | 18 A |
| 25 | 69 A | 36 A | 35 A | 30 A |
| 50 | 139 A | 72 A | 70 A | 60 A |
| 75 | 208 A | 108 A | 104 A | 90 A |
| 100 | 278 A | 144 A | 139 A | 120 A |
| 150 | 416 A | 217 A | 209 A | 180 A |
| 200 | 555 A | 289 A | 278 A | 241 A |
| 250 | 694 A | 361 A | 348 A | 301 A |
| 315 | 874 A | 455 A | 438 A | 379 A |
| 500 | 1388 A | 722 A | 696 A | 601 A |
| 630 | 1749 A | 909 A | 876 A | 758 A |
| 1000 | 2776 A | 1443 A | 1391 A | 1203 A |
Frequently asked questions
How many amps is 1 kVA?
1 kVA equals 8.33 A at 120 V and 4.17 A at 240 V single-phase, 2.78 A at 208 V three-phase and 1.20 A at 480 V three-phase. Internationally it is 4.35 A at 230 V single-phase and 1.44 A at 400 V three-phase.
How do I convert kW to kVA?
Divide kW by the power factor. For example, 40 kW at a power factor of 0.8 is 40 ÷ 0.8 = 50 kVA. If the power factor is 1 (purely resistive load), kW and kVA are equal.
Why are generators rated in kVA?
A generator’s losses and heating depend on the current it supplies, which is set by kVA. The real power it can deliver (kW) depends on the load’s power factor, which the manufacturer does not control, so the rating is given in kVA, usually with kW at 0.8 power factor.
What voltage should I use for three-phase calculations?
Use the line-to-line voltage, such as 400 V or 415 V in Pakistan, the UK and Europe, or 208 V or 480 V in the United States.
Related calculators and guides
These calculators give engineering estimates for planning and learning. Final designs must follow your local code (NEC, IEC/BS 7671, PEC or the authority having jurisdiction) and be checked by a qualified electrical engineer or licensed electrician.