Portlandia Electric Supply · Technical Team · Updated September 4, 2026

kVA-to-amps is the conversion behind nearly every transformer, generator, and commercial inverter specification. Unlike our kVA-to-kW guide — which is about power factor — this conversion ignores power factor entirely, because kVA already includes it. What you need instead is voltage. Enter kVA and volts in the calculator below and get full-load amps instantly, for both single-phase and three-phase systems.

Apparent power S (in VA) equals voltage times current. Solve for current and scale kVA up by 1,000:

Single-phase: A = kVA × 1,000 ÷ V
Three-phase: A = kVA × 1,000 ÷ (√3 × V_LL)

The √3 (≈1.732) in the three-phase formula accounts for the 120° phase displacement between the three conductors: in a balanced three-phase system the total power is √3 × V_LL × I, not 3 × V × I. Use line-to-line voltage — 208, 480, or 600 V — in that formula. If your nameplate shows line-to-neutral voltage (120, 277, 347 V), the equivalent form is A = kVA × 1,000 ÷ (3 × V_LN), which returns the same per-phase amps.

The inverse conversion — amps to kVA — is the same algebra reversed: kVA = A × V ÷ 1,000 (single-phase) or kVA = A × V × 1.732 ÷ 1,000 (three-phase). And if you need the watts side of the story, that requires power factor: kW = kVA × PF, covered step-by-step in our kVA-to-kW conversion guide.

Table 1 — Single-phase full-load amps: A = kVA × 1,000 ÷ V.

Table 2 — Three-phase full-load amps per phase: A = kVA × 1,000 ÷ (1.732 × V_LL). Rows use standard transformer sizes.

Transformers (NEC Article 450)

Every dry-type transformer nameplate is denominated in kVA, and NEC 450.3 protection rules key off rated current — which you must compute from kVA and voltage. A 75 kVA, 480 V three-phase transformer carries 90.2 A full-load secondary current. That number drives the secondary breaker (125 A at 125%), the conductor size (at least 1/0 AWG copper at 75 °C before adjustments), and the fault-current calculations downstream. Standard dry-type sizes — 15, 30, 45, 75, 112.5, 150, 225, 300, 500 kVA — exist precisely so these amp values land on serviceable equipment.

Generators

Standby generators are specified in kVA because the alternator's thermal limit is set by current, not real power. A 100 kW / 125 kVA unit (0.8 PF) at 480 V three-phase delivers 150.3 A — that is the figure your transfer switch, feeders, and breaker must carry. Undersizing here is one of the most expensive field mistakes; our generator sizing guide walks the full load-side process.

Commercial solar inverters

String and central inverters in the 50–350 kW class carry kVA ratings (typically kVA = kW at unity PF, with headroom for reactive support per IEEE 1547). A 125 kVA inverter at 480 V three-phase outputs 150.3 A AC — the input to your interconnection study, AC combiner sizing, and NEC 705.12 busbar loading calculation. Pair this with our NEC 690 disconnect guide for the protection side.

A field note on nameplate literacy

Transformer and generator nameplates pack the inputs for this conversion into a few compact lines: kVA rating, primary and secondary voltages, phase, impedance (%Z), and frequency. The impedance percentage deserves a mention even though it does not enter the full-load conversion — it caps the available fault current, which is why a 75 kVA, 4%Z transformer at 208 V can only deliver about 5.2 kA into a bolted fault (208.2 A ÷ 0.04). Full-load amps tell you what the equipment carries; impedance-limited amps tell you what it can deliver into a short, and breaker interrupt ratings (AIC) are chosen against the latter.

• NEC 450.3 (Transformers): overcurrent protection is expressed as percentages of rated current — you must convert kVA to amps before the table means anything. Primary-only protection can reach 125% (with secondary protection) or up to 250% in supervised arrangements.
• NEC 240.6 (Standard ratings): after the 125% continuous multiplier (210.20, 215.3), round up to 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400 A and beyond. The calculator above does this step automatically.
• NEC 220 (Load calculations): service and feeder loads are computed in VA; converting to amps at the service voltage is the final step before selecting service equipment.
• NEC 445 / 702 (Generators, optional standby): generator feeders are sized from nameplate current — derived from kVA and voltage exactly as above.

Once amps are known, conductor selection goes through the NEC 310.16 ampacity chart, and overcurrent devices through our breaker sizing guide.

Table 3 — Standard three-phase dry-type transformers at 480 V: full-load amps, 125% design current, and the NEC 240.6 overcurrent device.

Table 4 — Running the formula backward: kVA = A × V ÷ 1,000 (1φ) or A × V × 1.732 ÷ 1,000 (3φ). Useful when a switchgear schedule lists amps but the transformer catalog lists kVA.

• kVA to kW Conversion (Power Factor Guide)
• Amps to Watts Converter Guide
• kWh to Amps Guide
• Wire Ampacity Chart (NEC 310.16)
• NEC Wire Sizing Guide
• Breaker Sizing: NEC 125% Rule
• Whole-Home Generator Sizing Guide
• Transfer Switch Sizing Chart
• Solar Disconnects & Overcurrent Protection
• Shop Transfer Switches
• Shop Circuit Breakers
• Shop Commercial Standby Generators
• 100–125 A Transfer Switches
• Shop Commercial Solar Inverters

Sizing a transformer, generator, or commercial inverter? Get a quote from Portlandia Electric Supply — we stock commercial generators, transfer switches, and commercial inverters with full spec support.