Gear Module Calculator

About this calculator

The module of a gear is the fundamental sizing unit used in metric gear design — it's defined as the pitch diameter divided by the number of teeth (m = PD / N), and it determines how large each tooth is. Two gears can only mesh correctly if they share the same module, which is why it's the first number specified on any gear engineering drawing. This calculator also derives the related circular pitch (the arc distance between corresponding points on adjacent teeth) and diametral pitch (the imperial equivalent, teeth per inch of pitch diameter).

Mechanical engineers, machinists, and gear manufacturers use module calculations constantly when designing gearboxes, selecting off-the-shelf gears, or reverse-engineering a replacement part from a broken original — measuring the pitch diameter and tooth count of an existing gear lets you compute its module and order or cut a matching one. Standard module values (1, 1.5, 2, 2.5, 3, and so on) are defined by ISO 54 to keep gears interchangeable across manufacturers.