Diametral Pitch Calculator

The diametral pitch calculator quickly converts between module, diametral pitch, and circular pitch. 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.


Only one parameter (module, diametral pitch, or circular pitch) is required to calculate the other two. The unused boxes will be disabled until the entered text is deleted or cleared

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Convert Module to Diametral Pitch

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

Convert Diametral Pitch to Module

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

Convert Diametral Pitch to Circular Pitch

A gear's Circular Pitch is 3.1415 divided by its Diametral Pitch (technically it's π/DP, but in practice four decimal places are usually sufficient). That is, a gear with a diametral pitch of 16 would have a corresponding circular pitch of 0.1963. The units for circular pitch are typically inches

How are Gear Pitch and Module Related?

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

Here's a Quick Summary:

DP = 25.4/Mod

Mod = 25.4/DP

CP = 3.1415 / DP

From worm and worm gears to hobs and lathes, pitches can be expressed and equated between these units. This calculator will keep you from digging around in books, and keep you designing or making gears in your shop. Whether you're designing a single gear, or looking to calculate a gear ratio, we have the tools you need to get started.