Three-Phase Power Calculator
Find the real power, current or voltage of a balanced three-phase load — and get the apparent power (kVA), reactive power (kVAR) and the line current you need for breaker and wire sizing.
Three-Phase Power, Made Practical
Three-phase power runs almost everything industrial — motors, chillers, pumps, large HVAC. This calculator answers the question you actually have: how much current will this load draw (so you can size the breaker and wire), or how much power a given voltage and current represent. Enter what you know and solve for the rest.
That is real power in watts, using line-to-line voltage VL, line current IL and power factor PF. Apparent power (what the utility and your conductors actually see) drops the power factor:
and reactive power is Q = √(S² − P²) in kVAR. Rearranging the first equation gives the line current for sizing: IL = P / (√3 × VL × PF).
Wye vs Delta
The power formulas above use line quantities and are the same for both connections. What changes is what each phase sees. In a wye (Y) connection the phase voltage is VL / √3 and the phase current equals the line current. In a delta connection the phase voltage equals VL and the phase current is IL / √3. The calculator reports both per-phase values.
Worked Example
A 480 V load drawing 50 A at 0.85 power factor: P = 1.732 × 480 × 50 × 0.85 = about 35.3 kW, with S = 41.6 kVA. For continuous duty you would size conductors and the breaker for 50 × 1.25 = 62.5 A.
Applications
- Motor circuits — find full-load current to size feeders and overloads.
- HVAC & chillers — convert nameplate kW or kVA to current draw.
- Generators & transformers — check kVA loading against rating.
- Panel & feeder sizing — turn a load in kW into the amps your wire must carry.
- Power factor correction — see the reactive power you are paying to move.
Frequently Asked Questions
Do I use line or phase voltage?
Use line-to-line voltage (the number on the nameplate, like 208 V, 480 V) with line current. The √3 factor already accounts for the three phases.
What if I do not know the power factor?
Motors at full load are often around 0.85–0.9; lightly loaded motors are lower. Resistive loads (heaters) are 1.0. If unsure, 0.85 is a common planning value.
Why is apparent power (kVA) larger than real power (kW)?
Power factor below 1 means current and voltage are out of phase, so conductors carry more current than the real power alone would suggest. Wire and breakers are sized to kVA / current, not kW.
Related calculators
- Ohm’s Law Calculator — voltage, current, resistance and power for single loads.
- Voltage Drop Calculator — check conductor voltage drop over a run.
- Wire Size Calculator — minimum conductor size from load current.
- More electrical & engineering tools on the Engineering hub.