Gear Module Calculator
Find gear module from pitch diameter and tooth count — or pitch diameter from module and teeth — along with outside diameter, root diameter, and circular pitch.
Enter your values
Choose what you know, then enter the other two values.
How this calculator works
Module is the standard size parameter for metric gear teeth — the pitch diameter divided by the number of teeth:
Once module and pitch diameter are known, the tooth proportions follow standard full-depth conventions: addendum a = m, dedendum b = 1.25m, giving outside diameter D + 2m and root diameter D − 2.5m. Circular pitch (tooth spacing measured along the pitch circle) is p = π·m.
Standard module series (ISO)
| Series | Values (mm) |
|---|---|
| Coarse pitch | 1, 1.25, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20 |
| Fine pitch | 0.3, 0.4, 0.5, 0.7, 0.8, 1 |
Using a standard module lets a gear mesh with off-the-shelf cutters, hobs, and mating gears from other sources.
Frequently asked questions
Do both gears in a mesh need the same module?
Yes — two gears can only mesh correctly if they share the same module (or the same diametral pitch, in imperial systems) and a compatible pressure angle.
How is module related to diametral pitch?
Module (metric) and diametral pitch (imperial) both describe tooth size; they're related by module (mm) ≈ 25.4 / diametral pitch (teeth per inch).