Pitch Converter

The pitch converter shows equivalent numbers for imperial and inch systems like module, diametral pitch, circular pitch and threads per inch. A gear's pitch and number of teeth determine the overall size of the gear (and the blank you need to make that gear). A Gear Dimension Calculator can give you all of the physical dimensions on the gear (diameters and lengths of features on the teeth). However, for quick conversions between diametral pitch, module, and circular pitch, the Gear Pitch Calculator is the easiest. This is often helpful knowledge when reverse engineering an existing gear.

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A gear's Diametral Pitch is 25.4 divided by its Module. That is, a gear with a module of 2 would have a corresponding diametral pitch of 12.7. Keep in mind, the units for diametral pitch are 1/in

A gear's Module is 25.4 divided by its Diametral Pitch. That is, a gear with a diametral pitch of 16 would have a corresponding module of 1.5875. Keep in mind, the units for module are mm

A gear's Circular Pitch is π divided by its Diametral Pitch. That is, a gear with a diametral pitch of 16 would have a corresponding circular pitch of 0.1963. Here we use inches; in metric, CP (mm) = π × module (mm).

A gear’s equivalent Threads per Inch (TPI) is 1 / circular pitch (inches) for single-start threads. For an N-start worm, TPI = N / circular pitch. (Note: DP = π / CP.)
Also CP (mm) = π × module and equivalently module = CP / π.

As the module of a gear increases: the diametral pitch decreases, the circular pitch increases, and the size of the gear increases