kW to Amps Calculator — Free Online Calculator
Convert kilowatts (kW) to amps for single-phase and three-phase circuits. Free online kW to amperage converter with power factor.
How to Use This Calculator
Enter the power in kilowatts, voltage, and select your circuit type. Adjust the power factor for AC circuits (default 0.85 for typical mixed loads).
The Formula Explained
For DC: Amps = (kW × 1000) / Volts. For single-phase AC: Amps = (kW × 1000) / (Volts × PF). For three-phase AC: Amps = (kW × 1000) / (Volts × √3 × PF).
From Power to Current: The Inverse Calculation
Converting kilowatts to amps answers one of the most common electrical sizing questions: how much current does a given power load draw, so I can size the wire and breaker? The formula depends on voltage, phase configuration, and power factor. At its core: amps equals watts divided by volts, with adjustments for three-phase and reactive loads. Getting this right is essential for every service sizing, motor circuit design, and load calculation.
The calculation also reveals why higher voltage is better for high-power applications. A 100 kW load at 240V draws 417 amps single-phase. The same load at 480V draws 208 amps. At 4,160V (medium voltage distribution) it draws just 24 amps. This is why utilities distribute at high voltage and step down near the load — the wire savings across miles of transmission are enormous. The same principle applies in buildings: 480V three-phase distribution for motor loads saves dramatically on copper compared to 208V.
Worked Example: Sizing a 50 kW Generator Feeder
A 50 kW natural gas generator serves an emergency power panel at 480V three-phase, 0.8 rated power factor. Apparent power: kVA = 50 / 0.8 = 62.5 kVA. Current: 62,500 / (sqrt(3) × 480) = 75.2 amps.
NEC 215.2(A)(1) requires feeders to be sized at 125% of continuous load. 75.2 × 1.25 = 94 amps minimum conductor ampacity. Round up to a standard conductor: 1 AWG copper (110A at 75°C) is comfortable. Main breaker at the emergency panel: 100 amp. Transfer switch rated 100 amp minimum.
Note: generator nameplates often list kW AND kVA separately. Use the kVA for feeder sizing (which determines actual current) and kW for load matching (which determines if the generator can handle the load).
Worked Example: Electric Water Heater Sizing
A 50-gallon electric water heater with a 5,500W element. At 240V single-phase (standard residential), current = 5,500 / 240 = 22.9 amps. This is purely resistive so power factor is 1.0 and no adjustment needed.
Circuit sizing: NEC 422.13 treats water heaters as continuous loads (operate more than 3 hours), so the circuit must be 125% of the load: 22.9 × 1.25 = 28.6 amps. Next standard breaker size is 30A. Conductor: 10 AWG copper (30A at 75°C) is the standard residential water heater wire. A 4,500W element would give 18.75 amps × 1.25 = 23.4 amps, still needing a 25A or 30A breaker and 10 AWG wire.
Common mistake: using a 20A breaker with 12 AWG wire for a 4,500W heater. 18.75A is below 20A, seems fine — but the 125% continuous load rule requires 25A minimum, so 12 AWG and 20A breaker is a code violation.
Five kW-to-Amps Mistakes
1. Forgetting to convert kW to W. The formula uses watts, not kilowatts. Always multiply kW by 1000 first, or divide by 1000 at the end, depending on how you arranged the equation. Easy to forget.
2. Using wrong voltage on three-phase. 480V systems are line-to-line 480V but line-to-neutral 277V. The three-phase formula uses 480V.
3. Ignoring power factor on AC motor loads. A 10 kW motor at 0.8 PF draws 25% more current than a simple kW/V calculation suggests. Important for wire and breaker sizing.
4. Forgetting the 125% continuous load rule. NEC requires 125% sizing for loads operating 3+ hours. Water heaters, EV chargers, HVAC, commercial lighting all trigger this.
5. Confusing nameplate HP vs electrical input kW. Motor nameplate HP is mechanical output. Electrical input is higher due to efficiency losses. 10 HP = 7.46 kW mechanical output, but about 8.6 kW electrical input at 87% efficiency.
Quick Reference for Common Scenarios
120V single-phase (resistive): 1 kW = 8.33 amps. 2 kW = 16.67 amps. 1.8 kW = 15 amps (max on 15A circuit).
240V single-phase (resistive): 1 kW = 4.17 amps. 5 kW = 20.8 amps. 10 kW = 41.7 amps. 15 kW = 62.5 amps.
208V three-phase (resistive, per phase): 10 kW = 27.8 amps. 50 kW = 139 amps. 100 kW = 278 amps.
480V three-phase (resistive, per phase): 10 kW = 12.0 amps. 100 kW = 120 amps. 500 kW = 601 amps.
Divide by PF for inductive loads: a 100 kW motor load at 0.85 PF on 480V three-phase draws 120 / 0.85 = 141 amps per phase.
Code References
NEC Article 220 covers load calculations, specifying standard methods for residential, commercial, and industrial services. NEC 210.19 and 215.2 govern the 125% continuous load rule for branch circuits and feeders. NEC 430 covers motor circuit sizing using nameplate FLA rather than calculated values.
NEC Table 310.16 gives the ampacity values you use to translate calculated amps into wire sizes. Remember the 75°C column usually governs because of terminal ratings, not the 90°C column. NEC 240.6 lists standard breaker sizes — you round calculated amps up to the next standard size.
kW to amps: sizing service equipment from kilowatt loads
Commercial and industrial spec sheets rate equipment in kilowatts. To pick a breaker, transformer, or service size, you need amps. The math is watts-to-amps with the kilo prefix, but the practical context is different: you are usually sizing 480 V three-phase service, not a 120 V branch.
The formula and what it does
For 480 V three-phase: I = (kW x 1000) / (480 x 1.732 x PF) which simplifies to I = kW x 1.203 / PF. Mental math: 480 V 3-phase amps = kW x 1.2 / PF. For 208 V 3-phase: I = kW x 2.78 / PF.
Worked example
Scenario: 75 kW rooftop AC unit on 480 V three-phase.
PF for a large packaged HVAC is about 0.85. I = 75,000 / (1.732 x 480 x 0.85) = 106 A. NEC 440.32 requires 125 percent of largest motor: 132.5 A. Conductor: 1/0 AWG copper THHN at 75 C handles 150 A. Breaker: 150 A. Disconnect: 200 A non-fused.
Common mistakes to avoid
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For 208 V three-phase, what is the rule of thumb?
At PF 1.0: I = kW x 2.78. At PF 0.85: I = kW x 3.27. So 50 kW at 208 V PF 0.85 draws 163 A, almost 2.5x the same load at 480 V.
Why do industrial buildings prefer 480 V?
Lower current for the same power. Smaller conductors, smaller transformers, lower losses. The tradeoff is step-down transformers for 120 V loads.
How do I handle locked-rotor amps?
NEC 430.52 sizes branch-circuit OCPD based on locked-rotor, not running. Time-delay fuses or inverse-time breakers tolerate startup transients. Calculator gives running amps; LRA sizing is separate.
What if the load is given in horsepower?
1 hp = 0.746 kW. Use NEC 430.250 tables for motor amperage; those are what code requires for motor branch-circuit sizing.
Does the calculator handle delta vs wye?
Line-current math is identical for either at the same kW. Phase currents differ but line current (what you size service to) is the same.
How precise are nameplate kW ratings?
Resistive loads within 5 percent. Motors and compressors within 10 percent. HVAC varies more. For sizing, use highest published kW for the application.