well im getting an American football jersy new off ebay and i need to know what size i am, different places say different things

im a 38 inch chest that's the main bit

what size shall i get?
Jackson KE 3 Trans Black
Schecter C7 ATX
Siggery Custom

Axe Fx Owner
Im brought an XXL one over the net and its MASSIVE on me! then again i am around a medium size.....tbh i dont know why i did it now.

Still i love my Cowboys jersey even if it is like a tent on me