A full sew-in weave with virgin hair, would need approximately 8-10 ounces of hair. We recommend buying 3 bundles of hair for lengths 14" to 18". We recommend 4 to 5 bundles for lengths 20" or longer. Each bundles weigh 3.5 ounces. Rule of thumb " The longer the hair, the shorther the weft". Machine weft can use lesser amounts depending on the desired fullness.