So I ordered a M, it's large and loose on me - exactly the fit I wanted.
It is not an ideal running sweatshirt if I'm being honest, it's too thick; therefore wicked hot and bulky; therefore heavy during the run! Whilst running the hoodie part doesn't stay in place; you've got to adjust the strings accordingly. Keeping mind (which I clearly am aware of) this sweatshirt isn't for running purposes specifically!
However, for a modest sweatshirt and what I intended it for was perfect!