I order XL if I want it to fit under another shirt, a 2XL if i want to wear it loose untucked.  My chest is about 47".  My sleeve length is 34".  Sleeve length is right on with the XL, a tad long on the 2XL, but because of banded sleeve cuffs, not a problem.  I typically order 2xl polos and xl undershirts - so sizing is as expected.