NECKLACE LENGTHS: The common approximation is to allow a half inch of drape per inch of necklace length, so if your neck measures 13 inches, a 16-inch necklace will drape about 1.5 inches below the base of your throat. If your build is larger or smaller than average, you may wish to size up or down accordingly.
Chain lengths - How will it look? When purchasing finished chains the most common options are 16", 18", 20". These are the first three lengths shown. Longer chains can create a whole different look. Check out our chain by the inch section. Add jump rings and a clasp and you have a custom chain. It is easier than you may think. http://www.beaducation.com/shop/chain-jump-rings-chain-c-62_252.html