Gear Drive Motor Mass Moment of Inertia Equation:

Use these equations and calculator to determine the Inertia of a gear drive system. For any change in rotation speed, the load inertia will reflect back through the gears to the motor.

Gear Drive System
Gear Drive System


Motor Speed

Motor Speed Formula


Motor Speed Formula Alternate

Motor Torque:

Motor Torque Formula

Reflected Load Inertia

Reflected Load Inertia

Total Inertia realized at Motor:

Total Inertia realized at Motor


Sm Motor Speed, rpm
Sl =   Load Speed, rpm
Nl =   Number teeth on load gear
Nm Number teeth on motor gear
N =   Gear Ratio
Tm Torque of Motor, lb-in
Tl Torque of Load, lb-in
e =  Efficiency
Jl  Load Inertia, lb-in.-sec2
Jm = Drive Motor Inertia, lb-in.-sec2
Jr = Reflected Load inertia, lb-in.-sec2
Jt = Total Inertia, lb-in.-sec2