The number of bundles varies by client and their desired style.  Generally speaking, for a natural-looking sew-in, a minimum of two bundles is needed.  However, consideration should be given to the length chosen, the size of the head as well as the style. For a fuller look, three or more bundles would be in order.  Typically, lengths 18"+ require three bundles. Wearing a closure, frontal or 360 frontal will usually reduce the number of bundles needed.