“Pulleys and belts have two uses; to increase or reduce speed or torque, or to transfer power from one shaft to another. If the transfer of power is all you need, then two pulleys of the same diameter will do the trick. But most of the time you’ll also want to take the opportunity to trade speed for torque, or vice versa. This is done by using pulleys of different pitch diameters.”
Timing belts and timing pulleys are all around us. From airplanes to children’s toys, from agriculture to industrial production, timing pulleys keep our lives spinning. When you have a project and need to determine what type of timing pulley and timing belt you will need, how does that process work? Speed and torque may be provided by pulleys with various pitch diameters, but how do you find the belt length required for your application?
We know this is complex and daunting, so we have provided the answers to help you fully understand the timing pulleys, timing belts, timing stock, and all the other necessary components you need.
Terms to Know
Before we get into the details, there are several terms that we need to know to help streamline this process and maximize our understanding:
- Timing Belt Pulley: Timing belt pulleys work with timing belts to create a synchronous, non-slip transmission of movement. Also referred to as a drum or sheave, the timing belt pulley supports changes in belt direction or movement.
- Timing Pulley Bar Stock: Timing pulley bar stock is a length of sturdy material with pulley teeth machined in, which can be used to create custom pulleys. Timing pulley stock is ideal for prototypes or for wider-than-normal pulley applications.
- Pitch: The distance between the teeth on the timing belt pulley.
- Pitch diameter: The pitch diameter of a pulley is not the same thing as the outside diameter. Pitch diameter is quite difficult to determine because the pitch diameter is impossible to directly measure. The pitch diameter of any pulley is measured at tiny fibers inside the belt. So, the pitch diameter of a pulley depends not just on the pulley itself, but on the cord’s position within the belt. Pitch diameters from IPG can be found here.
- Major diameter/outer diameter: The diameter from the outer most part of the pulley circumference to the outer most part of the pulley on the other side.
- Belt Length: The measurements for the belt, the circumference, or the belt size is the belt length. The easiest way of determining the belt length is to reference the belt’s part number or description. IPG has a blog post on how to do that here. An alternative way to measure the circumference of any belt is to roll it along the wall, measuring the distance you’ve traveled once you get back to the same point on the belt.
Now that we have all of our terms down, we can get to the formula for our pitch diameter calculator.
Belt Length Calculator Formula:
First, how can we determine belt length?
The length of the belt is dependent on the diameters of both pulleys and the between their centers, the diameter of the first pulley, and the diameter of the second pulley. Like this: 
C = Center distance of the two pulleys
D1 = Pitch Diameter of Larger Pulley
D2 = Pitch Diameter of Smaller Pulley
Click here to see our available timing pulley diameters.
Now you are ready!
You now have the information you need to make an informed decision for your next custom timing pulley project. We have an assortment of available pitches and can customize if you do not find what you need. We also provide a variety of materials to make your timing pulley for any use. Check out our available materials here.
Contact us for more information on timing pulleys, pitch calculations, custom projects or any questions you have regarding your needs.