Three-Phase Motor Power & Current Calculator
By Santaji GadepatilinUpdated October 27, 2026
A motor's nameplate kW is its shaft output, but the supply must also cover losses and reactive current. That is why the current drawn is higher than kW alone suggests. See how to work out motor full-load current (FLC) and how to calculate three-phase power. This free three-phase motor power & current calculator solves for whichever value you leave blank and shows the formula and steps.
Line current (A) vs Rated output (shaft) power (kW) — other inputs held at your current values.
How to use the three-phase motor power & current 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.
For more background, read Motor Efficiency Classes (IEC 60034).
Three-phase motor power & current 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.
Current at different voltages
For a 11 kW motor (pf 0.85, efficiency 90%):
| Line voltage | Full-load current |
|---|---|
| 380 V | 21.8 A |
| 400 V | 20.8 A |
| 415 V | 20.0 A |
| 440 V | 18.9 A |
| 480 V | 17.3 A |
| 690 V | 12.0 A |
Single-phase vs three-phase
| Single-phase | Three-phase | |
|---|---|---|
| Power formula | P = V × I × pf | P = √3 × VL × IL × pf |
| Typical use | Homes, small motors under 2–3 kW | Industrial motors and large loads |
| Torque | Pulsating | Smooth |
Starting current
Direct-on-line (DOL) starting draws 6–8 times the full-load current briefly. Star-delta starters reduce it to about one-third, and soft starters or VFDs reduce it further. Size cables, fuses and generators to cope with starting current.
Power factor correction
Motors draw reactive power that does no useful work but loads cables and transformers. Adding capacitors raises power factor towards 0.95–0.98, reducing current and, in many tariffs, electricity charges.
Apparent, real and reactive power
- Apparent power S (kVA) = √3 × V × I
- Real power P (kW) = S × pf
- Reactive power Q (kVAr) = √(S² − P²)
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.
What is the current of a 7.5 kW motor at 415 V?
About 14 A, assuming 0.85 power factor and 88–90% efficiency.
Why is √3 used in three-phase power?
Because line voltage is √3 times phase voltage in a balanced three-phase system.