Belt Length Calculator
To find that number on your own, you need to use the belt length formula: Belt length = π/2 × (DL + DS) + 2L + (DL - DS)2/ (4L), where: DL is the diameter of the larger pulley (here 20 inches); DS is the diameter of the smaller pulley (here 6 inches); and. L is the distance between the center of the pulleys. Diameter of the large pulley.