Formula to find belt or chain length
D + d x 1.57 + 2x cd = belt length
Add diameter of big pulley or sheave or sprocket plus diameter of small pulley or sheave or sprocket, take this number times 1.57 (This gives you the extra for the wrap). Measure from center of one shaft to the center of the other shaft,
then double it. Now take you wrap and add it the the doubled center distance and you have you belt length.
Note that if you are using pitch diameters on a v-belt sheave you will need to use the pitch diameter on your v-belt.
When using this for figuring a chain length, if you will need to use the pitch diameter of the sprocket for the most precise measurement.
10" driven sheave
5" drive sheave
Belt length is 71.55" ( I normally round up or down depending on weather my adjustment is in or out when the shaft center measurement was taken.)