How to Size Timing Belts and Pulleys | Step-by-Step Tutorial

In this tutorial we walk through how to size timing belts and pulleys from the requirements up, instead of just grabbing a catalog number and hoping it works.
We start by defining the speed and torque the drive actually needs. From there we solve the pulley ratio for torque, then size the pulleys to hit the required linear belt speed. Next we pick the smaller pulley tooth count so the ratio still holds, and finally we size the belt using the standard length equation:
L = 2C + π(D₁ + D₂)/2 + (D₂ − D₁)² / (4C)
Whether you’re designing a linear axis, a conveyor, a rotary indexer, or just replacing a drive that never quite felt right, this is the practical process I use.

Hardware used here:
Belts: https://amzn.to/4x0jCGS
Pulleys:
https://www.mcmaster.com/products/1277n721/
https://www.mcmaster.com/products/1277n732/

We’ll cover:
Defining speed and torque requirements
Solving pulley ratio for torque
Sizing pulleys for linear speed
Choosing the smaller pulley by tooth count
Calculating belt length from center distance

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