The amount of bundles/hair packs necessary for a full head sew-in are solely variant upon the lengths of the bundles you are purchasing. Since each bundle is the exact same in weight, keep in mind that the longer the hair, the shorter the width of the weft. Here is our guide: Hair 12” through 18” in length: We recommend a minimum of 2 bundles/packs, though 2 should most often times cover your full head sew-in. We recommend 3 bundles if you are seeking a very full look. Note: We also recommend one lace closure if you are wanting to cover up your own hair or in the event you are bald, balding, or thinning out in the front or top of your head. Hair 20”+ in length: We recommend a minimum of 3 bundles, though 3 bundles will most often times cover your full head sew-in. We recommend 4 to 5 bundles if you are seeking a very full look. Note: We also recommend one lace closure if you are wanting to cover up your own hair or in the event you are bald, balding, or thinning out in the front or top of your head.