Take your actual body measurements as they are more accurate than measuring over your clothes.

Chest: Measure the chest around the fullest part, place tape close under the arms, making sure the tape is high on the shoulder blades

Sizes are approx.

Chest	S	M	L	XL	2XL	3XL
Inches	34-36"	36-38"	38-40"	40-42"	42-44"	46-48"