Motor Power Calculator
Convert mechanical power: torque × speed, or HP to kW.
Calculator
No signup required. Results are indicative—verify for your standards.
Mechanical shaft kW from torque, or convert mechanical HP to kW.
From T & n: 18.85 kW
Formula
P_kW = 2π × n/60 × T / 1000 = (2π × RPM × T) / 60000, with T in N·m, n in RPM. Also 1 hp (mechanical) ≈ 0.7457 kW.
Example calculation
1500 RPM, 120 N·m: P = (2π × 1500 × 120) / 60000 ≈ 18.85 kW. HP equivalent: 18.85 / 0.7457 ≈ 25.3 HP.
Engineering notes
Account for motor efficiency and service factor when selecting VFD or starter. Starting torque and duty cycle may require oversizing.
When to use this calculator
- Motor selection — calculate the required shaft kW from load torque and speed before selecting a motor frame
- VFD sizing — determine rated kW for variable frequency drive procurement from torque-speed requirements
- HP to kW conversion — convert imported equipment HP ratings to kW for Indian MCC and power schedules
- Conveyor and crusher drives — compute drive power from known pull force and belt or shaft speed
- Pump and fan driver sizing — verify motor rating against calculated hydraulic or aerodynamic power requirements
Frequently asked questions
- What is the difference between shaft power and motor input power?
- Shaft power (mechanical output power) is what the motor delivers at its shaft — the useful work. Motor input power = Shaft power / Motor efficiency. IE2 motors typically have 88–93% efficiency, IE3 motors 90–95%. Always size the motor based on the required shaft power, then confirm the input power for electrical design. For example, a load requiring 18.85 kW shaft power needs a 22 kW motor (next standard frame) with input of about 22/0.92 ≈ 23.9 kW at full load.
- What service factor should I apply when selecting a motor?
- Service factor (SF) accounts for intermittent overloads. Most industrial motors have SF = 1.15 (15% overload capacity for short periods). For design: do not rely on service factor for continuous duty — size the motor so the rated shaft power exceeds the maximum continuous load. Apply a design margin of 10–25% above the calculated load power for selection of the motor frame size.
- How do I convert horsepower to kW for Indian motor schedules?
- 1 mechanical horsepower (hp) = 0.7457 kW. 1 metric horsepower (PS) = 0.7355 kW. Most Indian and international standards now use kW. For legacy equipment specified in HP: multiply HP × 0.7457 for kW. Common conversions: 5 HP = 3.73 kW, 10 HP = 7.46 kW, 15 HP = 11.19 kW, 20 HP = 14.91 kW, 25 HP = 18.64 kW, 50 HP = 37.3 kW.
- How is motor torque related to power and speed?
- T (N·m) = P (kW) × 1000 × 60 / (2π × RPM) = 9549 × P (kW) / RPM. A motor running at 1500 RPM with 18.85 kW output produces 120 N·m. At 750 RPM (2-pole motor on 50 Hz), the same power produces 240 N·m — torque doubles when speed halves at constant power. This relationship is critical for selecting gear reducers, couplings, and drive shafts.