Wonderful shirt in excellent condition! 100% cotton.  Not marked but I am calling it a LARGE.  Full cut here. Please be sure to check your measurements below.

Armpit to armpit: 23

Shoulder to should across the back: 18

Overarm from shoulder seam to cuff: 27

Underarm from armpit seam to cuff: 22

Length from center back to hem: 30.5

Thanks for looking and please be sure to check out my other listings!