How to Calculate Gear Pitch

Gears' pitch and tooth sizes define their interaction with other gears.
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The diametral pitch of a gear describes how densely its teeth are set around it. The pitch is the ratio between the number of teeth and the gear's size, and engineers always express it as a whole number. This value is important for further calculations involving the gear, including the size of each of the gear's teeth. A smaller pitch corresponds with larger teeth, and smaller teeth belong on a gear with a larger pitch.

    Measure the radius of the gear. Exclude the gear's teeth from your measurement. For this example, imagine a gear with a radius of 3 inches.

    Multiply this measurement by 2: 3 × 2 = 6 inches.

    Divide the number of teeth on the gear by this measurement. For example, if the gear has 28 teeth: 28 / 6 = 4.67.

    Round this figure to the nearest whole number: 4.67 is approximately 5, so the gear has a pitch of 5.


    • "Pitch" sometimes instead refers to the circular pitch, which is the distance between corresponding points on successive teeth. To find this value, divide pi by the diametral pitch. With this example: 3.142 / 5 = 0.628 inches.

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