Received very quickly from Marketplace seller. This is a nice quality heavyweight T-shirt which should wear well and be slow to go out of shape. Having said that, though I love it and rate it 5 stars for me personally, since I am a slim-ish female (size 12) suspect this shirt is cut a little on the snug side for male purchasers. I bought a medium, and it is a loose but not baggy fit on me.
Advizable I think to take the 38" - 40" measurement as an exact fit, if you are between these two chest sizes the shirt will be close fitting.
Which is precisely why I bought the men's - I wanted loose fit. Delighted to find that it does fit me the way I wanted, but if you are a guy you might consider purchasing a size larger than your usual if you don't want it too snug.