That measurement doesn't seem right...I don't use apothecary jars but I believe the 16 oz should be closer to 4" in width. I can't give you any insight on the Joy wax, but if your jar is 4" across you may be looking at 2 CD12s. Maybe 2 CD14s, depending on the Joy wax and the FO (the heavier, spicier oils will often require you to wick up). Anyway, hope this helps some, and I am sure others with experience with Joy and with apothecaries will chime in. Also, make sure to do a search on testing, because you will do lots of it and want to make sure you are doing it right!