Aaron Marino of alpha m. diagrams the acceptable zone a man’s shirt should hit. The rise of the pant and the zones 1 – 4 are keys to the diagram.
Men’s tee shirts should fall no lower than zone 2. If it’s too short, the top of pants or underwear will be visible. Button-up dress shirts should hang low past zone 4 so that it doesn’t become untucked. Casual button-up dress shirts (worn untucked) should fall no lower than zone 3.