Motor Torque-Speed and Efficiency Calculator

Formula

• T (N·m) = 9550 × P (kW) / N (rpm)
• Peak torque at base speed (constant torque region)
• Torque at max speed (constant power region)

About this calculator

Part of our EV & Renewable Calculators collection. Battery sizing, solar panel tilt, wind turbine performance, and EV drivetrain estimates.

How it works

Peak torque uses the standard 9550 rule: torque in N·m equals 9550 times power in kW divided by speed in RPM. Torque at max speed shows the constant-power region. Efficiency band spans from peak minus 2% up to peak across partial load.

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

150 kW motor, base 4000 rpm, max 12 000 rpm.

1. Peak torque = 9550 × 150 / 4000 = 358 N·m
2. Torque at max = 9550 × 150 / 12 000 = 119 N·m

Result: 358 N·m peak, 119 N·m at max speed.

When to use

• Sizing EV traction motor torque at base speed
• Checking constant-power region torque
• Quick motor comparison at equal power

Limitations

• Uses standard 9550 constant (9549.3 exact)
• Does not model field weakening or gear ratio
• Efficiency band is illustrative ±2% from peak

FAQ

Where does 9550 come from?

T = P/ω = P/(2πN/60). With P in kW and N in rpm, the constant is 60×1000/(2π) ≈ 9550.