Size S M L XL 2XL 3XL 4XL
Chest Width 19" 21" 23" 25" 27" 29" 31"
Length 26" 27.5" 29.5" 30.5" 32" 33.5" 34.5"

 
Measure the width across the shirt about 1" below the armpit seam with the shirt laid flat.

Measure the length from the neck seam down to the bottom-back of the shirt.