This has lost its size tag at some point, but based on my own men's medium R1 tops I think this is a small or maybe xs.
Pit to pit = 52cm Top of neck to hem = 72cm Pit to cuff = 58cm
There is a hole at a seam in the back of the shirt, and where the sizing tag was removed from the neck - although this one doesn't go through both layers of fabric. Both easily sewn. Still in great useable condition because the fabric is otherwise excellent in all the usual high-wear areas like shoulders, elbows and cuffs.