Electrical
Single-phase current calculation from kW, voltage, and power factor
Calculate single-phase AC current from real power, load voltage, and power factor while avoiding phase-factor, unit, motor-efficiency, and equipment-sizing mistakes.
- Product
- Single-phase AC loads
- Level
- Field triage
- Read time
- 8 min
- Reviewed
- 2026-07-18
What to establish before troubleshooting
For a single-phase AC load, real power is P = V x I x PF. Rearranging for current gives I = (kW x 1,000) / (V x PF). Use the voltage measured or specified across the load, whether that circuit is connected line-to-neutral or line-to-line.
Do not include the square-root-of-three factor in a single-phase calculation. Use power factor 1.00 only for a load that can reasonably be treated as unity power factor; a lower power factor requires more current for the same real power and voltage.
If the entered power is motor shaft output rather than electrical input, account for efficiency before calculating current. Keep the result as a reasonableness estimate and use nameplate, manufacturer, and applicable electrical requirements for final decisions.
Abbreviated worked example
Calculate 2 kW at 120 V and 0.90 power factor
A single-phase load consumes 2.0 kW of real power at 120 V with a documented power factor of 0.90.
- 1Convert real power: 2.0 kW x 1,000 = 2,000 W.
- 2Current = 2,000 / (120 x 0.90) = 2,000 / 108.
Result: Estimated steady-state current is approximately 18.52 A.
Caution: This arithmetic does not determine conductor ampacity, overcurrent protection, motor starting current, or whether the measured waveform makes the stated power factor representative.
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