How do I convert HP to kW for a motor?

1 mechanical horsepower (HP) = 0.7457 kW. 1 metric horsepower (PS or CV) = 0.7355 kW. To convert HP to kW: multiply by 0.7457. To convert kW to HP: multiply by 1.341. Common conversions: 1 HP = 0.746 kW; 5 HP = 3.73 kW; 7.5 HP = 5.6 kW; 10 HP = 7.46 kW; 15 HP = 11.2 kW; 20 HP = 14.9 kW; 25 HP = 18.6 kW; 30 HP = 22.4 kW; 40 HP = 29.8 kW; 50 HP = 37.3 kW; 100 HP = 74.6 kW; 150 HP = 111.9 kW; 200 HP = 149.1 kW.

How do I calculate motor power from torque and RPM?

P (kW) = (2π × RPM × T) / 60,000, where T is torque in N·m and RPM is speed in revolutions per minute. Simplified: P (kW) = RPM × T / 9549. Example: conveyor shaft at 120 RPM, load torque 500 N·m: P = 120 × 500 / 9549 = 6.28 kW. Select a 7.5 kW motor (next standard frame). This formula works for any rotating machinery — pumps, fans, compressors, conveyors, mixers.

What is the difference between shaft power and motor input power?

Shaft power (output): the mechanical power delivered at the motor shaft — the useful work. Motor input power = Shaft power / Motor efficiency. IE2 motors: 88–93% efficiency. IE3 motors: 90–95%. Example: a load needing 18.85 kW shaft power with a 22 kW IE3 motor (92% efficiency) draws 22/0.92 ≈ 23.9 kW from the electrical supply at full load. Always calculate: required shaft kW → select next standard motor → calculate input kW for electrical design.

What service factor should I apply when selecting a motor?

Service factor (SF) is NOT a design margin — it indicates short-term overload capacity (typically SF = 1.15 for 15% overload). For continuous duty design: size the motor so rated shaft kW exceeds the maximum continuous load. Apply a design margin of 10–25% above the calculated load power when selecting the motor frame. For crushers, compressors, and loads with high starting torque: use 25–30% margin. For fans and centrifugal pumps: 10–15% is usually adequate.

How do I calculate motor torque from kW and RPM?

T (N·m) = P (kW) × 1000 × 60 / (2π × RPM) = 9549 × P (kW) / RPM. Example: 22 kW motor at 1450 RPM (4-pole, 50 Hz): T = 9549 × 22 / 1450 = 144.8 N·m rated torque. Starting torque is typically 1.5–2.5 × rated torque for DOL start. Full-load torque is the torque at rated kW and rated speed — the correct value to use for coupling and gearbox selection.

What standard motor speeds are available on 50 Hz supply in India?

Synchronous speeds on 50 Hz: 3000 RPM (2-pole), 1500 RPM (4-pole), 1000 RPM (6-pole), 750 RPM (8-pole), 600 RPM (10-pole), 500 RPM (12-pole). Actual full-load RPM is 2–5% below synchronous due to slip: a 4-pole motor at 50 Hz typically runs at 1450–1480 RPM. For the required speed, divide the load speed by the motor speed to get the required gear ratio, or specify a VFD to allow variable speed without a gearbox.

How do I size a motor for a VFD (variable frequency drive) application?

For VFD applications: (1) Calculate the maximum required shaft torque across the entire speed range. (2) At low speeds (below 30 Hz on 50 Hz supply), motor cooling is reduced — consider a forced-ventilated motor (IC416) or size up 1 frame for continuous low-speed operation. (3) The motor kW × VFD rated kW must match — do not pair a 22 kW motor with a 15 kW VFD. (4) For constant-torque loads (conveyors, compressors): size on torque. (5) For variable-torque loads (fans, pumps): size on rated duty point power; the motor is naturally lightly loaded at low speed.

What is the IE2 / IE3 / IE4 motor efficiency classification in India?

International Efficiency (IE) classes are defined by IEC 60034-30-1 and adopted in India via IS 12615 and BEE star ratings. IE1 (Standard): basic efficiency, no longer manufactured for most ratings. IE2 (High): minimum legal requirement under BEE for motors above 0.37 kW since 2017. IE3 (Premium): BEE 5-star rated, 1–4% higher efficiency than IE2, mandatory for motors above 37 kW in India from 2023 under Energy Conservation Act. IE4 (Super Premium): available in some ranges, 1–2% above IE3. Payback for IE3 over IE2 is typically 1–3 years for motors running above 4,000 hours/year.

Motor Power Calculator — HP to kW, Torque to kW & RPM Converter

Calculate electric motor shaft power (kW) from torque and RPM, convert HP to kW, and find torque from power and speed.

Calculator

No signup required. Results are indicative—verify for your standards.

Mechanical shaft kW from torque, or convert mechanical HP to kW.

Speed (RPM)

Torque (N·m)

Or mechanical HP → kW

From T & n: 18.85 kW

Formula

P_kW = (2π × RPM × T) / 60,000, with T in N·m, RPM in rev/min. Reverse: T = 9549 × P_kW / RPM. HP to kW: 1 mechanical HP = 0.7457 kW. Motor input kW = shaft kW / motor efficiency.

Example calculation

1500 RPM motor, 120 N·m load torque: P_shaft = (2π × 1500 × 120) / 60,000 ≈ 18.85 kW ≈ 25.3 HP. Motor input (η = 0.92): 18.85 / 0.92 = 20.5 kW. Select 22 kW standard frame motor.

Engineering notes

Standard motor synchronous speeds on 50 Hz supply: 3000 RPM (2-pole), 1500 RPM (4-pole), 1000 RPM (6-pole), 750 RPM (8-pole). Actual full-load RPM is 2–5% below synchronous due to slip. IE2 motor efficiency (IS 12615): 85–93% for 0.75–315 kW. IE3 (BEE 5-star): 87–95%. For VFD applications, size motor for maximum torque at minimum speed (reduced cooling at low speed). Service factor 1.15 is for intermittent overload only — do not use for continuous oversizing.

When to use this calculator

Motor selection — calculate required shaft kW from load torque and speed before selecting motor frame size
HP to kW conversion — convert imported equipment HP ratings to kW for Indian MCC and electrical schedules
VFD sizing — determine rated kW for variable frequency drive procurement from torque-speed requirements
Conveyor and crusher drives — compute drive power from belt pull force and pulley/shaft speed
Pump and fan driver sizing — verify motor nameplate rating against calculated hydraulic or aerodynamic power

Frequently asked questions

How do I convert HP to kW for a motor?: 1 mechanical horsepower (HP) = 0.7457 kW. 1 metric horsepower (PS or CV) = 0.7355 kW. To convert HP to kW: multiply by 0.7457. To convert kW to HP: multiply by 1.341. Common conversions: 1 HP = 0.746 kW; 5 HP = 3.73 kW; 7.5 HP = 5.6 kW; 10 HP = 7.46 kW; 15 HP = 11.2 kW; 20 HP = 14.9 kW; 25 HP = 18.6 kW; 30 HP = 22.4 kW; 40 HP = 29.8 kW; 50 HP = 37.3 kW; 100 HP = 74.6 kW; 150 HP = 111.9 kW; 200 HP = 149.1 kW.
How do I calculate motor power from torque and RPM?: P (kW) = (2π × RPM × T) / 60,000, where T is torque in N·m and RPM is speed in revolutions per minute. Simplified: P (kW) = RPM × T / 9549. Example: conveyor shaft at 120 RPM, load torque 500 N·m: P = 120 × 500 / 9549 = 6.28 kW. Select a 7.5 kW motor (next standard frame). This formula works for any rotating machinery — pumps, fans, compressors, conveyors, mixers.
What is the difference between shaft power and motor input power?: Shaft power (output): the mechanical power delivered at the motor shaft — the useful work. Motor input power = Shaft power / Motor efficiency. IE2 motors: 88–93% efficiency. IE3 motors: 90–95%. Example: a load needing 18.85 kW shaft power with a 22 kW IE3 motor (92% efficiency) draws 22/0.92 ≈ 23.9 kW from the electrical supply at full load. Always calculate: required shaft kW → select next standard motor → calculate input kW for electrical design.
What service factor should I apply when selecting a motor?: Service factor (SF) is NOT a design margin — it indicates short-term overload capacity (typically SF = 1.15 for 15% overload). For continuous duty design: size the motor so rated shaft kW exceeds the maximum continuous load. Apply a design margin of 10–25% above the calculated load power when selecting the motor frame. For crushers, compressors, and loads with high starting torque: use 25–30% margin. For fans and centrifugal pumps: 10–15% is usually adequate.
How do I calculate motor torque from kW and RPM?: T (N·m) = P (kW) × 1000 × 60 / (2π × RPM) = 9549 × P (kW) / RPM. Example: 22 kW motor at 1450 RPM (4-pole, 50 Hz): T = 9549 × 22 / 1450 = 144.8 N·m rated torque. Starting torque is typically 1.5–2.5 × rated torque for DOL start. Full-load torque is the torque at rated kW and rated speed — the correct value to use for coupling and gearbox selection.
What standard motor speeds are available on 50 Hz supply in India?: Synchronous speeds on 50 Hz: 3000 RPM (2-pole), 1500 RPM (4-pole), 1000 RPM (6-pole), 750 RPM (8-pole), 600 RPM (10-pole), 500 RPM (12-pole). Actual full-load RPM is 2–5% below synchronous due to slip: a 4-pole motor at 50 Hz typically runs at 1450–1480 RPM. For the required speed, divide the load speed by the motor speed to get the required gear ratio, or specify a VFD to allow variable speed without a gearbox.
How do I size a motor for a VFD (variable frequency drive) application?: For VFD applications: (1) Calculate the maximum required shaft torque across the entire speed range. (2) At low speeds (below 30 Hz on 50 Hz supply), motor cooling is reduced — consider a forced-ventilated motor (IC416) or size up 1 frame for continuous low-speed operation. (3) The motor kW × VFD rated kW must match — do not pair a 22 kW motor with a 15 kW VFD. (4) For constant-torque loads (conveyors, compressors): size on torque. (5) For variable-torque loads (fans, pumps): size on rated duty point power; the motor is naturally lightly loaded at low speed.
What is the IE2 / IE3 / IE4 motor efficiency classification in India?: International Efficiency (IE) classes are defined by IEC 60034-30-1 and adopted in India via IS 12615 and BEE star ratings. IE1 (Standard): basic efficiency, no longer manufactured for most ratings. IE2 (High): minimum legal requirement under BEE for motors above 0.37 kW since 2017. IE3 (Premium): BEE 5-star rated, 1–4% higher efficiency than IE2, mandatory for motors above 37 kW in India from 2023 under Energy Conservation Act. IE4 (Super Premium): available in some ranges, 1–2% above IE3. Payback for IE3 over IE2 is typically 1–3 years for motors running above 4,000 hours/year.

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