Three-Phase kVA to Amps Calculator
A dedicated three-phase converter with both voltage conventions: line-to-line (400V, 480V nameplates) and line-to-neutral (230V in a 400V system). The homepage kVA to amps calculator covers single-phase too.
Balanced three-phase load, using the line-to-line voltage on the nameplate.
The two three-phase formulas
Three-phase power can be written two equivalent ways, depending on which voltage your nameplate or meter gives you. Both describe the same physical system and must agree — if they don't, one of the voltages was read from the wrong pair of terminals.
Use the voltage measured between any two phases — 400V, 415V, 480V, 208V. This is the voltage on almost every equipment nameplate and the default in the calculator above.
Use the voltage from one phase to neutral — 230V in a 400V system, 277V in a 480V system. The 3 counts the three identical phase-to-neutral contributions.
Where √3 comes from
The three phases are sine waves spaced 120° apart. Add two of them together — which is what a line-to-line measurement sees — and the peaks do not simply double: they combine to √3 (≈ 1.732) times the single-phase voltage. That is why 230 V line-to-neutral and 400 V line-to-line are the same system seen from different terminals: 230 × 1.732 ≈ 400.
Total power is the sum over three identical phases: 3 × V(L-N) × I. Rewriting with V(L-L) = √3 × V(L-N) turns that into √3 × V(L-L) × I — the form used whenever the line-to-line voltage is the known quantity. The methodology page carries the full derivation.
Line-to-line or line-to-neutral?
Check where the voltage came from. Nameplates, generator data sheets and transformer plates quote line-to-line. A multimeter reading from one phase to the neutral bar gives line-to-neutral. European 400/230V and North American 480/277V and 208/120V systems are both described by the same pair of numbers — the larger is always line-to-line.
Mixing them up is the most common three-phase error: putting 230 V into the √3 formula understates the current by a factor of √3, and putting 400 V into the 3× formula overstates it the same way. When in doubt, compute both ways with a matched pair — the answers must meet in the middle.
Worked examples
A 250 kVA service at 208V three-phase: 250,000 ÷ (√3 × 208) = 250,000 ÷ 360.27 — 693.93 A per phase. Low voltage and big power means serious copper: the same load at 480V would draw 300.70 A.
A 45 kVA machine on a 415V three-phase supply (the South Asian standard): 45,000 ÷ (√3 × 415) = 62.60 A per phase — a 80 A-class breaker territory once starting current is considered.
Line-to-line: 100,000 ÷ (√3 × 400) = 144.34 A. Line-to-neutral: 100,000 ÷ (3 × 230) = 144.93 A. A whisker of difference from rounding 230.94 V down to 230 — the two formulas are the same statement.
Three-phase quick table
Per-phase amps for standard ratings at the three common line-to-line voltages. The full chart adds 120V and 240V columns and every rating in between.
| kVA | 208V · three-phase | 400V · three-phase | 480V · three-phase |
|---|---|---|---|
| 5 | 13.88 A | 7.22 A | 6.01 A |
| 10 | 27.76 A | 14.43 A | 12.03 A |
| 15 | 41.64 A | 21.65 A | 18.04 A |
| 25 | 69.39 A | 36.08 A | 30.07 A |
| 50 | 138.79 A | 72.17 A | 60.14 A |
| 75 | 208.18 A | 108.25 A | 90.21 A |
| 100 | 277.57 A | 144.34 A | 120.28 A |
| 250 | 693.93 A | 360.84 A | 300.70 A |
| 500 | 1,387.86 A | 721.69 A | 601.41 A |
| 1000 | 2,775.72 A | 1,443.38 A | 1,202.81 A |
Frequently asked questions
How do I calculate amps from kVA in three-phase?
Divide the kVA by the line-to-line voltage and by √3, in VA terms: amps = kVA × 1000 ÷ (√3 × V). Example: 100 kVA at 400 V is 100,000 ÷ (1.732 × 400) = 144.34 A per phase. That per-phase current is the figure breakers and cables are sized against.
What is 1 kVA in amps three-phase?
At 400 V three-phase, 1 kVA is 1.44 A. At 480 V it is 1.20 A, and at 208 V it is 2.78 A. Lower-voltage systems carry the same power at higher current, which is why 208 V services need heavier conductors than 480 V services of the same kVA.
Should I use 400V or 230V in the three-phase formula?
Both work, with different partners: 400 V is the line-to-line voltage and pairs with √3 (amps = kVA × 1000 ÷ (√3 × 400)); 230 V is the line-to-neutral voltage of the same system and pairs with 3 (amps = kVA × 1000 ÷ (3 × 230)). They give the same answer — 144.34 A for 100 kVA — because √3 × 400 and 3 × 230 describe the same system.
Why is there a √3 in the three-phase formula?
The three phase voltages sit 120° apart, so the voltage between any two lines is not twice the line-to-neutral voltage but √3 times it: 230 V line-to-neutral becomes 400 V line-to-line. Total power is 3 × V(L-N) × I, and substituting V(L-L) = √3 × V(L-N) gives √3 × V(L-L) × I. The √3 is geometry, not a fudge factor.
How many amps is 15 kVA three-phase?
At 400 V three-phase, 15 kVA is 21.65 A. At 480 V it is 18.04 A, and at 208 V it is 41.67 A. Watch the 208 V figure: a modest 15 kVA load already needs a 50 A-class circuit at that voltage once continuous-load rules are applied.
Sources and references
The three-phase identities and the standard voltages used here rest on the sources below; the methodology page derives them step by step.
- NFPA 70 — National Electrical Code (NEC) — the code electricians size conductors and protection against
- IEEE Std 141 — Recommended Practice for Electric Power Distribution (Red Book) — apparent power and load-current practice for industrial and commercial systems
- IEC 60038 — Standard Voltages — the standard voltage levels (120, 208, 240, 400, 480 V) used across this site
- NIST — SI unit of electric current (the ampere) — the definition of the ampere behind every result