Torque Calculator

How it works

1. 1Select your unit system — metric (kW, N·m) or imperial (hp, lbf·ft).
2. 2Enter the shaft power and the rotational speed in rpm.
3. 3The calculator applies T = P ÷ ω (where ω = 2πN/60) and displays the torque instantly.

Use cases

• Sizing electric motors and gearboxes for industrial machinery.
• Checking engine torque output from a dyno power and rpm reading.
• Verifying that a drive shaft or coupling can handle the expected load.

Frequently asked questions

What formula does this calculator use?

It uses T = P ÷ ω, where ω (angular velocity in rad/s) = 2π × N ÷ 60 and N is speed in rpm. For example, 10 kW at 1500 rpm gives ω ≈ 157.08 rad/s and T = 10 000 ÷ 157.08 ≈ 63.7 N·m.

How do I convert between N·m and lbf·ft?

1 N·m ≈ 0.7376 lbf·ft, so 63.7 N·m ≈ 47.0 lbf·ft. The calculator handles this conversion automatically when you switch to the imperial tab.

Why does the result show — when rpm is zero?

Torque from power is mathematically undefined at zero speed (division by zero). In practice, starting torque must be determined from the motor’s locked-rotor specification, not from steady-state power.