I would say anybody over 5 feet tall should be in a full size. I have sold 3/4 violins to some adults, but that is pretty rare. It actually can be swayed either way though if you have small or big hands. In the case of being 5 feet tall and you have small hands, I would suggest a 3/4 size. If you have normal sized hands (no short pinkies), I would suggest a regular 3/4 size. There also are options out there for 7/8 size violins although they are a lot less common. I do have some of these available through my store and many other dealers do as well.