Ordering the correctly sized belt is critical to the performance of the belt on your conveyor. A belt that is too long will quickly loosen and slip. A belt that is too short may be difficult to install and may shorten the belt's life. However it is generally far better to order a slightly smaller belt than a longer one, so err on the shorter side.
There are three ways to get the correct belt's length:
First you can cut an unused/new belt and measure the cut-length. If you are measuring a Twisted Belt, do not include the hook. If you measure a used belt, it will be stretched out and you will end up ordering a belt that is too long and will be too loose. We use cut-length to specify the belt's size, which corresponds to the belt's middle circumference. Do NOT use the outer or inner circumference, or you will order a belt that is much too long or too short.
Other names for Cut-Length: Middle Circumference, Pitch Circumference, OAL (Over-All Length). Do not use diameter, instead use this calculator to convert diameter into the cut-length.
Second you can use a string, winding it through the path that the belt will take through your conveyor or machine. When you have the string's length, use this calculator to get the belt's cut-length.
Third, if you have all the measurements and dimensions of the conveyor, including roller diameter and center-to-center distance, use this calculator to find the correct belt for your application.