Motor Gearbox Selector Calculator

Formula

• Power kW = Torque (N·m) × RPM × 2π ÷ 60,000
• Required power = Base power × Service factor ÷ Efficiency
• HP = kW × 1.341

About this calculator

Part of our Mechanical Calculators collection. Beams, bolts, springs, gears, bearings, and core ME calculations.

How it works

Motor power in kW equals torque times RPM times 2 pi divided by 60000. The service factor adds margin for duty cycle and load variation. Use the result to shortlist motor and gearbox combinations.

Enter your values in the inputs above and click CALCULATE. Results appear on the right without a page reload. No login and no server upload.

Worked example

120 N·m at 1450 rpm, service factor 1.25, drive efficiency 95%.

1. Base power = 120 × 1450 × 2π ÷ 60,000 = 18.2 kW
2. Required = 18.2 × 1.25 ÷ 0.95 = 24.0 kW
3. HP = 24.0 × 1.341 = 32.2 HP

Result: Select a motor at or above 24 kW (32 HP) before gearbox losses.

When to use

• Motor shortlisting from torque and speed requirements
• Adding duty cycle margin with a service factor
• Converting between kW and HP for catalog specs

Limitations

• Steady-state average power, not peak acceleration
• Does not select motor frame or thermal class
• Gearbox efficiency must be estimated by the user

FAQ

What service factor should I use?

Uniform load: 1.0 to 1.15. Moderate shock: 1.25. Heavy shock: 1.5 or higher. Follow manufacturer guidance for your application.

Motor power or gearbox input power?

This gives shaft power required at the load. Include gearbox efficiency so the motor is sized for losses in the drive.

How do I use this with the gear ratio calculator?

Use gear ratio to find output torque and speed, then use this tool to convert required torque and speed into motor power.