Three-phase power calculator
Line voltage, current and power factor: you get real, apparent and reactive power for a balanced three-phase load.
Real power
9.98 kW
- Real power9.98 kW
- Apparent power11.09 kVA
- Reactive power4.83 kvar
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How it's calculated (visible formula)
S = √3 × V × I; P = S × PF; Q = S × sin φ
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Measure or enter line-to-line voltage (480 or 208 V in the US).
- Measure current per phase with a clamp meter.
- Take power factor from the motor plate or an analyzer.
- Apparent power S = √3 × V × I.
- Real power = S × PF; reactive = S × sin φ.
Worked example: Motor at 480 V, 16 A, PF 0.9
- S = 1.732 × 480 × 16 = 13.3 kVA
- P = 13.3 × 0.9 = 12 kW
→ 12 kW, 13.3 kVA and 5.8 kvar.
Common mistakes
- Using line-to-neutral voltage with √3.
- Assuming PF 1 for motors.
- Adding kW and kVA directly.
Pro tips
- Check phases are balanced — measure all three currents.
- Correct reactive power with capacitors if your utility penalizes it.
- Size conductors from current, not kW.
- Pick starters and overloads for the full-load current.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- Why √3?
- Line voltage in three-phase is √3 times phase voltage.
- kW vs kVA?
- kW does work; kVA is what the wiring carries. kW = kVA × PF.
- What is reactive power?
- Power that sloshes between source and load; capacitors correct it.
- How many amps for a 10 hp motor at 480 V?
- About 14 A full-load current per NEC tables.
- Why is there reactive power?
- From magnetic fields in motors and transformers.
- 208 V vs 240 V three-phase?
- Use your actual line voltage in the formula.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.