Productive ToolboxElectric Motor Power Calculator
Calculate electric motor power, current, torque, and efficiency. Supports HP to kW conversion, three-phase and single-phase motors, and motor energy cost analysis.
Electric Motor Power Calculator
Calculate motor power from torque & speed, voltage & current, or horsepower. Get instant results in Watts, kW, and HP.
Actions
Calculation Mode
Mechanical Parameters
Torque in Newton-meters
Rotational speed in revolutions per minute
Motor Presets
Next step
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What Is an Electric Motor Power Calculator?
This electric motor power calculator works out a motor's power in watts, kilowatts and horsepower three ways: from shaft torque and speed, from the voltage, current, power factor and efficiency of a single-phase, three-phase or DC supply, or by converting a horsepower rating. Each result shows the working step by step.
The formulas below cover the related figures engineers check next — full-load current, input power, torque and kVA — with tables for common motor sizes at 400 V (Europe) and 480 V (North America).
Motor Power Formulas
Core Formulas
3-Phase Current (A) = kW × 1000 ÷ (√3 × V × PF × η)
1-Phase Current (A) = kW × 1000 ÷ (V × PF × η)
Input Power (kW) = Output kW ÷ Efficiency
Torque (N·m) = kW × 9,549 ÷ RPM
Apparent Power (kVA) = kW ÷ Power Factor
HP to kW = HP × 0.7457
Example: 7.5 kW motor, 400 V 3-phase, PF 0.85, η 90%
Current = 7,500 ÷ (1.732 × 400 × 0.85 × 0.90) = 14.2 A
- η (eta) — motor efficiency as a decimal (e.g. 90% = 0.90)
- PF — power factor, typically 0.75–0.95 at full load for induction motors
- √3 = 1.7321 — three-phase constant; omit for single-phase calculations
- 9,549 — constant = 60,000 ÷ (2π × 1,000) for torque in N·m from kW and RPM
How to Use the Electric Motor Power Calculator
Step-by-Step Guide
- 1Choose a calculation method: Pick Mechanical (torque and speed), Electrical (voltage and current) or Horsepower Conversion, or load a preset such as a 480 V or 400 V three-phase motor, a conveyor drive or a 24 V DC motor.
- 2Mechanical: enter torque and speed: Type the shaft torque in newton-meters and the speed in RPM. Power = 2π × RPM × torque ÷ 60.
- 3Electrical: enter the supply values: Choose single-phase AC, three-phase AC or DC, then enter voltage, current, power factor and efficiency from the nameplate. Three-phase uses the line-to-line voltage and the √3 factor.
- 4Read the power: The result shows the power in watts, kilowatts and horsepower, with each step of the working.
- 5Copy, export or save: Copy the result, download it as text or CSV, or reopen earlier calculations from the history.
What This Calculator Provides
- ✓Power from shaft torque and speed (RPM)
- ✓Power from voltage, current, power factor and efficiency
- ✓Single-phase AC, three-phase AC and DC supplies
- ✓Horsepower to watts and kilowatts
- ✓Results in W, kW and HP with step-by-step working
- ✓Presets for common motors
- ✓Copy, export as text or CSV, and history
- ✓Your inputs are not collected or stored
Worked Examples
Sizing a Conveyor Motor from Torque
A conveyor drive needs 36 N·m at 1,450 RPM. In Mechanical mode: P = 2π × 1,450 × 36 ÷ 60 = 5,466 W, or 5.47 kW (7.33 HP). With a 1.15 service factor the requirement is 6.3 kW, so the engineer picks the next standard IEC size, 7.5 kW.
Shaft Power of a US Three-Phase Pump
A pump motor on a 480 V three-phase supply draws 14 A at power factor 0.86 and 92% efficiency. In Electrical mode: P = 1.732 × 480 × 14 × 0.86 × 0.92 = 9,209 W, or 9.21 kW (12.3 HP) at the shaft, which confirms it is running close to its 15 HP rating.
Is a Premium-Efficiency Motor Worth It?
A 22 kW motor runs 6,000 hours a year at $0.10/kWh. An IE2 motor (91.4% efficient) draws 22 ÷ 0.914 = 24.07 kW and costs $14,442 a year; an IE3 motor (93.6%) draws 23.50 kW and costs $14,103. The $340 annual saving repays a $280 price difference in about 10 months.
Motor Power Reference Tables
HP to kW and Full-Load Current (3-phase, PF 0.85, η 90%)
| HP | kW (output) | Input kW | 400 V (A) | 480 V (A) |
|---|---|---|---|---|
| 1 HP | 0.75 kW | 0.83 kW | 1.4 | 1.2 |
| 2 HP | 1.49 kW | 1.66 kW | 2.8 | 2.3 |
| 3 HP | 2.24 kW | 2.49 kW | 4.2 | 3.5 |
| 5 HP | 3.73 kW | 4.14 kW | 7.0 | 5.9 |
| 7.5 HP | 5.59 kW | 6.21 kW | 10.6 | 8.8 |
| 10 HP | 7.46 kW | 8.29 kW | 14.1 | 11.7 |
| 15 HP | 11.19 kW | 12.43 kW | 21.1 | 17.6 |
| 20 HP | 14.91 kW | 16.57 kW | 28.1 | 23.4 |
| 25 HP | 18.64 kW | 20.71 kW | 35.2 | 29.3 |
| 30 HP | 22.37 kW | 24.86 kW | 42.2 | 35.2 |
| 50 HP | 37.29 kW | 41.43 kW | 70.3 | 58.6 |
Torque at Common Motor Speeds
| Power | 750 RPM | 1,450 RPM | 2,900 RPM |
|---|---|---|---|
| 0.75 kW | 9.5 N·m | 4.9 N·m | 2.5 N·m |
| 1.5 kW | 19.1 N·m | 9.9 N·m | 4.9 N·m |
| 3 kW | 38.2 N·m | 19.7 N·m | 9.9 N·m |
| 5.5 kW | 70.1 N·m | 36.2 N·m | 18.1 N·m |
| 7.5 kW | 95.5 N·m | 49.4 N·m | 24.7 N·m |
| 11 kW | 140 N·m | 72.4 N·m | 36.2 N·m |
| 15 kW | 191 N·m | 98.7 N·m | 49.4 N·m |
| 22 kW | 280 N·m | 145 N·m | 72.5 N·m |
* Torque = kW × 9,549 ÷ RPM. 1,450 RPM is typical for 4-pole 50Hz motors; 1,750 RPM for 60Hz.
Frequently Asked Questions
What is the formula for electric motor power?
3-phase: Output (kW) = √3 × V × I × PF × η ÷ 1000. Single-phase: Output (kW) = V × I × PF × η ÷ 1000. Input power = Output ÷ Efficiency.
How do I convert motor horsepower to kW?
1 HP = 0.7457 kW. Multiply HP by 0.7457 to get kW. Examples: 5 HP = 3.73 kW; 10 HP = 7.46 kW; 15 HP = 11.19 kW; 20 HP = 14.91 kW.
How do I calculate motor current from kW?
3-phase: I = kW × 1000 ÷ (√3 × V × PF × η). Single-phase: I = kW × 1000 ÷ (V × PF × η). Example: 7.5 kW at 400 V, PF 0.85, η 90% → I = 7,500 ÷ (1.732 × 400 × 0.85 × 0.9) ≈ 14.2 A.
What is motor efficiency?
Motor efficiency is shaft output power divided by electrical input power. A 90% efficient 10 kW motor consumes 11.1 kW. Efficiency drops at partial load — motors are most efficient at 75–100% of rated load.
How do I calculate motor torque from power and speed?
Torque (N·m) = kW × 9,549 ÷ RPM. Example: 5 kW at 1,450 RPM → 5 × 9,549 ÷ 1,450 = 32.9 N·m. In imperial: Torque (lb·ft) = HP × 5,252 ÷ RPM.
What is power factor in an electric motor?
Power factor is real power (kW) divided by apparent power (kVA). Motors typically have PF 0.75–0.95 at full load. It drops significantly at partial loads. Low PF increases current draw and conductor sizing requirements.
What is the difference between kW and kVA for motors?
kW is real power (actual work done). kVA is apparent power (total drawn from supply). kW = kVA × Power Factor. Generator and transformer sizing must use kVA, not kW.
Why is √3 used in three-phase motor calculations?
√3 (1.7321) is the three-phase constant that accounts for the phase relationship between the three supply conductors. Omitting it in three-phase calculations produces a result 42% too low.
How do I size a motor for an application?
Calculate required shaft output from the mechanical load (P = F × v or P = T × ω). Apply a 1.15–1.25 service factor. Select the next standard motor rating above the result from the IEC standard series: 0.37, 0.55, 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 22, 30, 37, 45, 55, 75 kW.
Is my data private when using this calculator?
Yes. We do not collect or store what you enter.
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