Convert kVA (kilovolt-amperes) to amps for single-phase and three-phase systems. Essential for sizing generator connections, transformer outputs, and electrical panel capacity.
✓ Verified: NEC 2023 — Transformer and Generator Sizing Standards — April 2026
kVA
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Apparent power in kilovolt-amperes (kVA)
V
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Output voltage (e.g. 120, 240, 480, 208)
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Single-phase or three-phase system
Convert kVA (kilovolt-amperes) to amps for single-phase and three-phase systems. Essential for sizing generator connections, transformer outputs, and electrical panel capacity.
Current (Amps)
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⚠️ Disclaimer: These calculations are for planning and estimation purposes only. Actual generator, transformer, and conductor sizing must comply with the NEC and local codes and be verified by a licensed electrical engineer or electrician.
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Sources & Methodology
✓ Formulas verified against authoritative sources listed below.
IEEE standard for transformer ratings and full-load current calculations from kVA and voltage
Methodology: Single-phase amps = (kVA x 1000) / V. Three-phase amps = (kVA x 1000) / (sqrt(3) x V) = (kVA x 1000) / (1.7321 x V). kVA is apparent power — no power factor needed since kVA already includes both real and reactive power. kW = kVA x PF.
⏱ Last reviewed: April 2026
How to Convert kVA to Amps
kVA (kilovolt-amperes) is the apparent power rating of generators, transformers, and UPS systems. Converting kVA to amps is straightforward because apparent power already incorporates both real and reactive components — no separate power factor input is needed. The amps produced depend only on the kVA rating and the output voltage.
The kVA to Amps Formula
Single-phase: Amps = (kVA x 1000) / Volts. Three-phase: Amps = (kVA x 1000) / (1.732 x Volts). Example: 10 kVA single-phase at 240V: A = 10000/240 = 41.67 amps. Same 10 kVA three-phase at 240V: A = 10000/(1.732 x 240) = 10000/415.7 = 24.06 amps. Three-phase always produces fewer amps per phase for the same kVA.
Why kVA is Used for Generators and Transformers
Generators and transformers must supply apparent power (kVA) to loads, which includes both the real power (kW) the load uses and the reactive power (kVAR) it needs. The current drawn from the generator depends on kVA, not kW. This is why a generator rated at 10 kVA at PF 0.85 can only deliver 8.5 kW of real power.
kVA Rating vs. kW Capability
The relationship: kW = kVA x Power Factor. A 10 kVA generator at 0.8 PF delivers 8 kW. At 0.9 PF, 9 kW. At 1.0 PF (resistive loads only), 10 kW. Never exceed the kVA rating even if your load seems to be within the kW rating — the generator current limit is set by kVA, not kW.
Transformer kVA and Secondary Current
Transformer secondary current = (kVA x 1000) / (Secondary Voltage). For a 25 kVA single-phase transformer with 120V secondary: I = 25000/120 = 208.3 amps. This is the maximum current the secondary winding can safely carry. NEC 450.3 requires overcurrent protection based on this full-load current.
1-Phase: A = (kVA x 1000) / V | 3-Phase: A = (kVA x 1000) / (1.732 x V)
No power factor needed — kVA is already apparent power (includes reactive component). kW = kVA x PF. kVAR = sqrt(kVA^2 - kW^2). Example: 25 kVA at 480V 3-phase: A = 25000/(1.732 x 480) = 30.07 A. 1 kVA = 1000 VA = 1000 volt-amperes.
kVA to Amps — Common Generator and Transformer Ratings
kVA
120V 1-Phase
240V 1-Phase
208V 3-Phase
480V 3-Phase
5 kVA
41.67 A
20.83 A
13.88 A
6.01 A
10 kVA
83.33 A
41.67 A
27.76 A
12.03 A
15 kVA
125.00 A
62.50 A
41.63 A
18.04 A
25 kVA
208.33 A
104.17 A
69.39 A
30.07 A
45 kVA
375.00 A
187.50 A
124.90 A
54.13 A
75 kVA
625.00 A
312.50 A
208.17 A
90.21 A
100 kVA
833.33 A
416.67 A
277.56 A
120.28 A
250 kVA
2,083 A
1,042 A
693.9 A
300.7 A
⚡ Generator Sizing Tip: When sizing a generator for mixed loads, total all load kVA (not kW) and add a 20-25% safety margin. Motor starting currents can be 6-8x running current, so the generator must handle starting surges. For a single large motor, add the motor kVA at starting (usually 6x running kVA) to the running load of all other equipment.
Frequently Asked Questions
Single-phase: Amps = (kVA x 1000) / Volts. Three-phase: Amps = (kVA x 1000) / (1.732 x Volts). No power factor is needed because kVA already represents apparent power.
It depends on voltage. 10 kVA at 120V single-phase = 83.33 amps. At 240V single-phase = 41.67 amps. At 480V three-phase = 12.03 amps.
kW (kilowatts) is real power that does useful work. kVA (kilovolt-amperes) is apparent power — the total power the source must supply including reactive power. kW = kVA x Power Factor. A 10 kVA generator at PF 0.8 can supply only 8 kW of real power.
Generators are rated in kVA because the current they can safely produce depends on kVA, not kW. The generator's alternator windings are limited by current (heating), and current is determined by kVA and voltage. The kVA rating also avoids confusion when different power factor loads are connected.
Single-phase: A = 25000/240 = 104.17 amps. This is the transformer's full-load secondary current at 240V. Three-phase: A = 25000/(1.732 x 240) = 60.10 amps per phase.
Single-phase: kVA = (A x V) / 1000. Three-phase: kVA = (A x V x 1.732) / 1000. Example: 50 amps at 240V single-phase: kVA = (50 x 240)/1000 = 12 kVA.
Only when power factor = 1.0 (purely resistive loads). For all other loads, kVA is larger than kW. kW = kVA x PF. Most practical loads have PF between 0.75 and 0.95, so kVA is typically 5-25% higher than kW.
A = 100000/(1.732 x 480) = 100000/831.4 = 120.28 amps. This is the full-load current for a 100 kVA transformer or generator with 480V three-phase output.
Full-load amps = 10000/240 = 41.67 A. NEC requires overcurrent protection at 125% of continuous load: 41.67 x 1.25 = 52.08 A. Use a 60A breaker (next standard size above 52A).
Only if the power factor is 1.0 (purely resistive load). For most loads with PF 0.85: maximum kW = 10 kVA x 0.85 = 8.5 kW. Never load a generator beyond its kVA rating even if the kW seems within limits.