Not sure where I ended up buying this one but I cut off most of the tag years ago. I wear a Medium or Large usually and this one fits me just fine so based on the measurements below I'd say most likely a Large but if your Medium it should be totally fine. Under the armpit area looks a little color faded but common after washing it over the years. (see pics)

Measures roughly 19 inches wide and 26 inches long.

I have 8 cats so there might be a few pieces of hair on shirt but I did my best to clean it off :)