How many shirts?

How many shirts should a man have? I suppose the obvious answer is how many shirts do I wear a week? And how often do we do laundry?

I need work shirts and casual shirts, and we obviously don't want to be washing and ironing every other day!

Thomas Fink, in The Man's Book suggests that the number of shirts required for any specific purpose is equal to the square root of the number of days involved. That would mean 19 shirts in total. 15 would be work shirts, and as I change when I get home that would mean 34 shirts in total - eeek! But I don't necessarily put on a clean shirt every day (is that bad?) as I work in an air conditioned office, so maybe I can get away with 7 work shirts, and 10 casual shirts?

At least trousers are simpler...