Small - 27-32" waist 

Medium - 29-34" waist 

Large - 31-36" waist 

Extra Large - 33-38" waist 

Hammer wears a size 29 / Medium (deep pleat) and is 6'1"

Clint wears a size 32 / Medium (moderate pleat) and is 5'11"  

Joe wears a size 34 / Medium (no pleat) and is 5'7" 

Size is a construct, wear what feels good.