There are a couple of effective methods for shrinking a shirt, and one of the easiest is by boiling it. Simply heat up a pot of water, and then shut off the stove as soon as it reaches a boil. Drop the shirt in the water immediately, and then let it sit for about five minutes.
If you’re looking for a more serious degree of shrinkage, you can leave the shirt in the water for up to 20 minutes. The longer the shirt is left in the water, the further it will shrink, but obviously, there’s a limit to this magic. Most shirts will only shrink up to a maximum of 20% in size.
Once you’re finished soaking the shirt, remove it from the water using a pair of tongs or a wooden spoon. Once the shirt has cooled off enough to touch, wring it out and examine your progress. The boiling process can be repeated as many times as you need to achieve the desired results.