How many shirts should a man have?

maybe 20.

Really depends on the individual. If one is a Lawyer one needs more dress shirts than a plumber. It also depends on how active one is. One wants to be able to go at least weeks w/o laundering if possible. Thus if one works out regularly you need 14 plus T-shirts alone. 11 Dress shirts (assuming 5 working days a week and one spare. And probably 14 or so casual shirts depending to some extent if you always change your shirt on getting home from work. Add on two formal shirts just in case two formal occasions come up back to back. So I think the answer should be close on 40 rather than 20.