Three-Phase Motor Power & Current Calculator
By Santaji GadepatilinUpdated October 27, 2026
Line current (A) vs Rated output (shaft) power (kW) — other inputs held at your current values.
How to use this calculator
The defaults show an 11 kW motor on 415 V — the full-load current is calculated. You can also enter a measured current to find the power being drawn. Use the motor’s nameplate values for power factor and efficiency where possible.
The formulas
Pin = √3 × V × I × cos φ Pout = Pin × η
Worked example
11 kW motor, 415 V, cos φ = 0.85, efficiency 90%:
- Pin = 11 ÷ 0.90 = 12.22 kW
- I = 12,222 ÷ (1.732 × 415 × 0.85) = 20.0 A
Approximate full-load currents at 415 V
| Motor | Current |
|---|---|
| 1.5 kW | ~3.3 A |
| 5.5 kW | ~11 A |
| 11 kW | ~20 A |
| 22 kW | ~40 A |
| 45 kW | ~80 A |
Actual values vary by manufacturer and efficiency class — always check the nameplate.
Practical notes
- Starting current of a direct-on-line motor is typically 6–8× full-load current.
- Cable sizing must account for both current and length — check with the cable voltage drop calculator.
- For single-phase, use P = V × I × cos φ instead.
Frequently asked questions
What is the formula for three-phase power?
P = √3 × V × I × cos φ, where V is the line-to-line voltage and I the line current. Shaft power is this multiplied by efficiency.
Why does a motor draw more current than the kW rating suggests?
The kW rating is shaft output. The supply must also cover motor losses (efficiency) and reactive current (power factor), so input current is higher.
What is a typical power factor?
Around 0.80–0.90 at full load for standard induction motors. It drops sharply at light load.