Belt lengths vary depending on pulley sizes and how the machine and motor are mounted on the table. Parts lists can not account for all these variances.
With a little elementary math like 5th or 6th grade and a ruler or tape measure, you can determine the required belt length.
First step, before measuring, is to set the motor belt tension adjustment at half way so you have room to tighten or loosen the belt tension when installing your new belt.
Measure diameter of the pulleys at the edge of the rim assuming you are buying the proper width of belt for the pulley, take half the circumference of the pulleys, write the total down. Place the ruler or other straight edge against the pulley rims and measure the distance between the contact points on the pulleys. Only need to measure 1 side since the opposite side will be the same, double that measurement and add it to the total for the half circumferences you wrote down. The total of these is the belt length (outside measure) you need.