How do I calculate motor torque from kW and RPM?

Torque in N·m equals power in watts divided by angular speed in radians per second.

Is motor kW electrical input or shaft output?

This calculator uses mechanical shaft power. Electrical input also depends on efficiency and power factor.

Can this calculate starting torque?

No. Starting torque requires the motor and driven-load torque-speed curves.

Does this include gearbox losses?

No. Apply measured or manufacturer efficiency separately when translating across a gearbox.

Motor Torque, Speed and Power Calculator

Solve one mechanical shaft quantity from the other two, with simultaneous metric and imperial results. Electrical input, starting torque and gearbox losses are separate.

About this calculator

Quick Calculator inputs above give an instant result; use Advanced fields (factors, units, or decoding) when your datasheet differs from defaults.

Example: 15 kW at 1500 RPM → shaft torque ≈ 95.5 N·m (T = 9550 × P / n).

Result explanation / How to use: treat values as screening only. Engineering assumption and disclaimer: confirm nameplate limits, OEM selectors, and site conditions before procurement or programming.

Hub: Protection calculators — continue related sizing from this topic cluster.

Torque–speed–power calculator

Solve for

Input units

Shaft power (kW)

Shaft speed (RPM)

Mechanical shaft result

Formula and boundary:

Use actual shaft speed rather than synchronous speed when calculating rated torque. This calculator does not predict acceleration, pull-out torque, efficiency or motor heating.

Motor FLA → VFD sizing → Starter guide →

Your Calculation Path

motor torque speed powerCalculate motor FLA →

Continue Your Calculation

Translate shaft demand into motor current or drive selection using nameplate efficiency and PF.

Power and torque relationship

The shared core uses angular velocity exactly: P = Tω and ω = 2πn/60. The familiar 9550 constant is a rounded metric shortcut.

Primary reference: Siemens motor technical documentation for rated power, speed and torque.

Frequently Asked Questions

What does 9550 mean?

It combines watts-to-kW and RPM-to-radians-per-second conversions in the rounded equation T = 9550P/n.

Should I enter synchronous RPM?

Use measured or rated shaft RPM for actual shaft torque; induction motors run below synchronous speed.

Can I enter horsepower?

Yes. Select imperial input; results still show both hp/kW and lb-ft/N·m.

Does this size a motor?

No. Duty cycle, acceleration, thermal limits and load torque must also be checked.