While it is not easy to control the amount a T-shirt shrinks, cotton T-shirts generally do shrink when washed and dried at very hot settings. To make sure a shirt is not shrunk too much, pull it out, and check it at regular intervals during the process.
Wash the T-shirt
Turn the T-shirt inside out to protect any decoration. Wash it with the washing machine set to hot water with a hot rinse.
Dry the T-shirt on high
Put the T-shirt, still inside-out, into the dryer. Set the dryer on its highest setting and dry the T-shirt.
Check the T-shirt
Pull the T-shirt out of the dryer at regular intervals to check on the shrinking process. Some T-shirts shrink quickly, while others are treated with chemicals to prevent them from shrinking much. When the T-shirt has reached the desired size, pull it out of the dryer.