Calculating Drive Belt Length
Given two pulleys, a known distance apart. The diameter of each pulley is known. This page calculates the length of the belt required to wrap both pulleys with no slack. You can also enter a belt length, and calculate the distance required between pulleys. This program does not take into account stretch or wear of belt or pulleys.
Note: If there is a large size difference between the two pulleys, you may want to avoid minimum spacing between them as this will decrease the wrap length around the smaller pulley, decreasing it's loading capability.