eyeing the weight of weed is by no means an accurate game. If you dont have a scale, you prety much have to trust the guy selling it to you. roughly speaking.. 1/16 of an ounce would be about 1.5" x 1.5" if its in fairly small pieces pushed into a square on a table. If its in 1 nugget, its kind of hard to explain.. you just sorta know by looking at it from experience.

ps. iv never heard of anyone buying a 1/16th. why not just get a dub?