if you’re ordering team, tri gear, make sure you ask if they’re using pro-fit or relaxed fit etc. There are different “mediums”.
I’m a 38"chest, 32" waist and wear a Small in LG Tri jerseys (they stretch, a lot, I think we have the monaco model) and a Medium in the cycling top. The small cycling top is too tight for me, but the Medium is a bit roomier than I like.
On the other hand, I’ve gotten a LG jersey from Serotta and it was baggy beyond belief. I sold it since I could never really use it.