Buying a necklace and need to know length to buy so it extends to my pecks/nipple line?

I am looking to buy a necklace and would like to know the lenth to buy so the end of the necklace piece extends to my pecks/nipple line. I am about 6'0'' if that helps and looking at a necklace that is 24 inches long with a 1.5 pendant size. Any help would be appreciated. Thanks.