What is the formula for three-phase motor power?

The active (real) power consumed by a three-phase motor is P = √3 × V_L × I_L × cos φ × η, where V_L is line voltage, I_L is line current, cos φ is power factor, and η is motor efficiency. Without η, the formula gives shaft input power.

What is the difference between kW, kVA, and kVAR?

kW is active (real) power that does useful work. kVA is apparent power — the total power drawn from the supply. kVAR is reactive power used to maintain magnetic fields. They form the power triangle: S² = P² + Q², where S is in kVA, P in kW, and Q in kVAR.

What is a typical power factor for an electric motor?

Typical power factor for induction motors at full load is 0.80–0.90. At partial loads, PF drops significantly — a motor at 25% load may have PF as low as 0.40–0.55. Synchronous motors can operate at unity or even leading power factor.

What is motor efficiency and how does it affect power calculation?

Motor efficiency η is the ratio of mechanical output power to electrical input power. Typical values: 85–96% for standard motors, depending on size. IE3 premium efficiency motors typically exceed 92%. Always include η when calculating electrical input from rated mechanical power.

How do I find motor current from nameplate power?

Rearrange the formula: I = P / (√3 × V × cos φ × η). For example, a 15 kW motor at 400 V, PF 0.85, efficiency 0.91 draws I = 15000 / (√3 × 400 × 0.85 × 0.91) ≈ 28.0 A.

Free Engineering Tool

Three-Phase Motor Power Calculator

Calculate active power P = √3 × V × I × cos φ × η for three-phase motors. Bidirectional — solve for any variable. Also shows apparent & reactive power.

IEC 60034 Bidirectional Power Triangle

Solve For

Line Voltage (V)

Line Current (A)

Power Factor cos φ (0–1)

Efficiency η (0–1)

Active Power (kW)

Quick presets

Results

Active Power P

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Apparent Power S

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Reactive Power Q

—

Line Current I

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Power Factor / Efficiency

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Three-Phase Power Formula

The active (real) power consumed or delivered by a three-phase AC circuit is:

P — active power (W or kW)
V_L — line-to-line voltage (V)
I_L — line current (A)
cos φ — power factor (0–1)
η — motor efficiency (0–1)

Power Triangle

Where S is apparent power (kVA), P is active power (kW), and Q is reactive power (kVAR).

Practical Example

Example — 15 kW Motor at 400 V

Given: P = 15 kW, V = 400 V, cos φ = 0.85, η = 0.91

I = P / (√3 × V × cos φ × η) = 15000 / (1.732 × 400 × 0.85 × 0.91) = 28.0 A

S = √3 × V × I = 1.732 × 400 × 28.0 = 19.40 kVA

Q = √(S² − P²) = √(19.40² − 15²) = 12.30 kVAR

💡 Tip: When calculating electrical input power from a motor’s rated mechanical output, always divide by efficiency η. The nameplate kW is typically the shaft (mechanical) output.

A reliable **three phase motor power calculator** is an essential tool for electrical engineers and technicians who need to quickly determine active, apparent, and reactive power values without performing manual computations. By inputting known parameters such as line voltage, line current, power factor, and efficiency, this three phase motor power calculator applies the standard formula P = √3 × V × I × cos φ × η to deliver accurate results in seconds. Its bidirectional functionality allows you to solve for any unknown variable, making it invaluable for motor sizing, load analysis, and energy auditing tasks.

Three Phase Motor Power Calculator | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 March 3, 2026

Results

Three-Phase Power Formula

Power Triangle

Practical Example