How many T-shirts do I actually need?

Fewer than most drawers hold. A practical everyday rotation is roughly seven to ten tees you genuinely like — enough to get between washes without wearing any one out fast, in colors that work with your trousers. Beyond that, extra tees mostly sit unworn, which is the opposite of good cost per wear: a tee you wear twice a year is expensive no matter what it cost. The better move is to replace worn-out favorites with a slightly better version rather than adding volume. Buy for the gaps in what you actually reach for, not for the sale.