The size of the poncho should be based on the size of the person wearing it and the size of their backpack. Most ponchos are around 60 inches wide when finished. The fabric usually comes in 60 inch widths from the mill. The poncho's usability and comfort are based on its size. All ponchos are designed to protect the body from rain and cold weather, but some people may want a bigger poncho to cover their backpack as well.