A full sew-in weave with Goddess Lengths Virgin Hair you would need approximately 8 to 10 ounces of hair. We recommend using 2 bundles of hair for lengths 12” to 16”. We recommend 3 bundles for lengths 18″or longer. Each bundles weighs approximately 3. 5 ounces. These are suggestions, but how many bundles you need solely depends on your own personal preference for thinness or thickness. Keep in mind the longer the length the thinner the bundle, which is why number of bundles for use varies.