A full sew-in weave with Virgin human hair, would need approximately 8 oz to 10 oz of hair. We recommend buying 2 packs of hair for lengths 14” to 18”. We recommend 3 packs for lengths 20″ or longer. Each pack of wefts weighs 3.5 oz. BE MINDFUL, As you gain length, you loose fullness. So up to 4+ packs may be needed for 30 inch wefts. Ponytail: For a ponytail, typically you only need 1 pack of wefts.