Three Phase Power Calculator
Calculate the real output power (kW) of a three-phase electrical system from line voltage, line current, power factor, and efficiency. Use it for motor sizing, generator selection, and load analysis.
Last updated: September 2026
Formula below · 2 sources (ieee.org, Wikipedia) · Updated Sep 2026
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About this calculator
In a balanced three-phase system the real power is P = √3 × V_LL × I_L × PF, where V_LL is the line-to-line voltage and I_L the line current. This holds for both wye and delta connections. Because V_LL = √3 × V_phase, the same power can be written P = 3 × V_phase × I_L × PF when you know the line-to-neutral (phase) voltage, for example 277 V on a 480Y/277 V system. Choose how you entered the voltage and the calculator uses the matching form, then multiplies by the system efficiency η to give output power: P (kW) = √3 × V_LL × I × PF × (η/100) / 1000, or 3 × V_phase × I × PF × (η/100) / 1000. Power factor (PF) accounts for reactive loads (motors, transformers) that draw current out of phase with voltage. Apparent power is √3 × V_LL × I / 1000 kVA.
How to use
Example: a motor on a 480 V three-phase supply, line current 20 A, power factor 0.85, efficiency 92%. Select "Line-to-line voltage". Step 1 — √3 ≈ 1.732. Step 2 — 1.732 × 480 × 20 × 0.85 × 0.92. Step 3 — 1.732 × 480 = 831.4; × 20 = 16,627; × 0.85 = 14,133; × 0.92 = 13,002 W. Step 4 — 13.0 kW of output power. Entering the phase voltage instead, 277 V with "Phase voltage", gives 3 × 277 × 20 × 0.85 × 0.92 / 1000 = 13.0 kW, the same answer.
Frequently asked questions
What is the difference between wye and delta connection in three-phase power calculations?
In a wye (star) connection each phase winding sits between a line and the neutral, so the phase voltage is the line voltage divided by √3 and the phase current equals the line current. In a delta connection each winding spans two lines, so the phase voltage equals the line voltage and the line current is √3 times the phase current. Either way, the total power in terms of line quantities is the same: P = √3 × V_line × I_line × PF. The connection matters for which voltage you measure, not for the power formula.
How does power factor affect three-phase power consumption and electricity bills?
Power factor is the ratio of real power (kW) to apparent power (kVA). A low power factor means the system draws more current than the actual work requires, increasing losses in cables and transformers. Utilities often charge commercial customers a penalty for power factors below 0.9 or 0.95. Improving power factor with capacitor banks reduces reactive current, lowers energy losses, and can eliminate utility surcharges — often paying back the investment within months.
Why is three-phase power more efficient than single-phase for industrial applications?
Three-phase systems deliver power continuously through three overlapping voltage waveforms, producing smoother torque in motors and allowing smaller conductors to carry the same power compared to single-phase. For the same apparent power, a three-phase system uses about 75% of the conductor material of an equivalent single-phase system. Three-phase motors are also simpler, more reliable, and more efficient than single-phase motors of comparable size, making them the preferred choice for pumps, compressors, and CNC machinery.