kVA to Amps Calculator

About the kVA to Amps Calculator

This kVA to amps calculator converts apparent power (kVA) into current (amps) for single-phase, three-phase, or DC electrical systems. Use it to size breakers and conductors from transformer or generator nameplates, select feeder cables for UPS systems, or verify motor amperage against expected current draw.

Built using the standard NEC formulas with default voltages and the √3 factor for common industrial three-phase systems (208V, 480V, 600V). Power factor is not part of this conversion — it relates kVA to kW, not kVA to amps.

How kVA to amps conversion works

Two formulas based on phase configuration:

3-phase: I = (kVA × 1000) ÷ (V × √3)
Single-phase: I = (kVA × 1000) ÷ V

For three-phase systems, divide kVA by line-to-line voltage times √3 (1.732). For single-phase, divide by line voltage directly. Note that power factor doesn’t appear in either formula — current is determined by apparent power (kVA), not real power (kW).

Worked example

A 50 kVA, 480V three-phase transformer delivers I = (50 × 1000) ÷ (480 × 1.732) = 60.1 amps at full nameplate load. To size the secondary breaker per NEC 450.3(B), use 125% of full-load current: 60.1 × 1.25 = 75 amps — round up to a standard 80A breaker.

Why kVA, not kW, for sizing

Equipment sized in kVA (transformers, generators, UPS, switchgear) is limited by current, not by load PF. A 50 kVA generator can deliver 50 kVA whether the load runs at PF 0.8 (40 kW) or PF 1.0 (50 kW) — what changes is how much useful work the load produces. Sizing in kVA means you size for current capacity, which is what determines wire gauge, breaker rating, and equipment thermal limits.

This is why generator and transformer nameplates always carry kVA ratings: the manufacturer is telling you how much current the equipment can carry, not how much real work it can do (which depends on the load).

When to use this calculator

• Sizing the main breaker for a 3-phase transformer or generator
• Selecting feeder conductors for a UPS by amp rating per NEC ampacity tables
• Verifying a motor nameplate kVA against actual measured amperage
• Quick checks during electrical inspections or maintenance
• Cross-referencing service entrance ratings to building load calculations
• Estimating short-circuit current contribution from a transformer (with %Z)
• Calculating soft-starter or VFD input current ratings

Common kVA-to-amps quick reference

• 1 kVA at 120V single-phase = 8.33 amps
• 1 kVA at 240V single-phase = 4.17 amps
• 1 kVA at 208V three-phase = 2.78 amps
• 1 kVA at 480V three-phase = 1.20 amps
• 1 kVA at 600V three-phase = 0.96 amps

Multiply by your transformer or generator kVA to get total current. Example: a 100 kVA, 480V 3-phase transformer = 100 × 1.20 = 120 amps full load.

Frequently Asked Questions

How do you convert kVA to amps for a 3-phase system?

Use I = (kVA × 1000) ÷ (V × √3). For 50 kVA at 480V three-phase: I = (50 × 1000) ÷ (480 × 1.732) = 60.1 amps. Apparent power converts directly to current using line-to-line voltage; power factor doesn’t enter the calculation.

What is the formula for single-phase?

I = (kVA × 1000) ÷ V. For 5 kVA at 240V single-phase: I = 5,000 ÷ 240 = 20.8 amps. No √3 factor for single-phase systems.

What is the difference between kVA and kW?

kVA is apparent power — total volt-amps in the circuit. kW is real power — the portion that does useful work. They relate through power factor: kW = kVA × PF. For most motors, PF is 0.8–0.95.

How many amps is 1 kVA at 120V single-phase?

I = (1 × 1000) ÷ 120 = 8.33 amps. At 240V single-phase: 4.17 amps. At 208V three-phase: 2.78 amps. At 480V three-phase: 1.20 amps.

Why are generators and transformers rated in kVA instead of kW?

Their thermal limit depends on current (and therefore apparent power), not on load power factor. A 50 kVA generator can deliver 50 kVA regardless of whether the load runs at PF 0.8 (40 kW) or 1.0 (50 kW). Sizing in kVA ensures you can deliver full current at any PF.

Should I use line-to-line or line-to-neutral voltage in the formula?

For three-phase calculations using I = (kVA × 1000) ÷ (V × √3), use line-to-line voltage (e.g., 208V, 480V, 600V). For single-phase, use the system voltage directly (120V, 240V).

How do I size a breaker from kVA?

Calculate full-load amps from kVA, then multiply by the NEC continuous-load factor (usually 1.25 for transformers per NEC 450.3(B), 1.25 for motors per NEC 430.22). Round up to the next standard breaker size. For 60 amps continuous: 60 × 1.25 = 75 amps → use 80A breaker.

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Sizing equipment after your conversion? Browse General Purpose motors, HVAC motors, or Pump motors from Baldor, WEG, and Marathon.

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