What is Gear Module?
Module is the single number that sets a gear's tooth size — what it means, how it's calculated, and how to pick one.
Module (m) is the standard metric measure of gear tooth size. It's defined as the pitch diameter divided by the number of teeth:
m = pitch diameter / teeth, or equivalently pitch diameter = m × teeth.
A bigger module means bigger teeth: more material per tooth, more strength, but a larger overall gear for the same tooth count. Every other tooth dimension scales directly off module — in the involute profile this site generates, addendum (tip height above the pitch circle) is exactly m, and dedendum (root depth below the pitch circle) is 1.25m. Halve the module and every one of those dimensions halves too.
Two gears can only mesh correctly if they share the same module (and pressure angle) — module is what makes the tooth pitch match up around the mesh point, regardless of how many teeth each gear has. That's why the catalog is organized by module first: every gear in the module 1 collection can mesh with every other gear in that same collection, at whatever ratio their tooth counts give you.
Picking a module
- Module 0.3 — very fine teeth, compact mechanisms, best suited to resin printing, precision laser cutting, or small instrument gearing.
- Module 0.5 — a good default for small 3D-printed or laser-cut mechanisms.
- Module 1 — a common general-purpose size; strong enough for light mechanical loads, still compact.
- Module 2 — noticeably stronger, larger teeth; suited to higher-torque or higher-wear applications.
See the Spur Gear Design Guide for how module interacts with tooth count and pressure angle, or jump straight to the module 1, 20-tooth gear as a concrete worked example.