How do you shrink cotton?

Cotton shrinks when wet and very hot, so the most effective way to shrink cotton is to wash it in the hottest water setting a washer offers, and then dry it with hot air. Another strategy is to boil it, since it is the same technique without the cleaning.

These methods do not shrink cotton clothing as much or as evenly if the garment is labeled "pre-shrunk." When washed in a washing machine, a garment's color may bleed onto other clothing, so it's best if it is washed either by itself or with clothing of the same or very similar color.