Sometimes a tee feels too big, and you may want it to shrink slightly. For 100% cotton, here are safe methods:
Hot wash + hot dryer
The most common approach. Wash inside out on high heat, then dry hot.
Boiling soak
Submerge the shirt in boiling water for 5–15 minutes, then dry on high heat.
Targeted shrinking
Use hot water and a hairdryer to shrink specific areas like sleeves or neckline.