Calculating Pitch Diameter for Synchronous Sprockets / Pulleys

If you know the number of sprocket grooves and the belt pitch (distance from the center of one belt tooth to the center of the next), you can easily calculate sprocket (or pulley) pitch diameter:

     Metric Pitch Belts / Sprockets:
     sprocket pitch diameter (in) = 0.012532 × pitch (mm) × # grooves

     Timing Belts / Pulleys:
     pulley pitch diameter (in) = 0.31831 × pitch (in) × # grooves

Pitch and number of grooves can typically be identified using the part number:

     Metric Pitch Example - 14MX-40S-68:
     sprocket pitch diameter (in) = 0.012532 × 14 mm × 40 grooves = 7.018 in

    Timing Example - TL40H150:
     pulley pitch diameter (in) = 0.31831 × 0.50 in × 40 grooves = 6.366 in