For the best fit, find a favorite t-shirt you own, lay it flat, and measure it from armpit to armpit (B).
  (B) WIDTH (inches) (A) LENGTH (inches)
S 21 ⅜ 18 ½
M 22 ¾ 19 ¼
L 25 ½ 20 ½
  (B) WIDTH (cm) (A) LENGTH (cm)
S 54.3 47
M 57.8 49
L 64.8 52
Product measurements may vary by up to 2" (5 cm).