This question gets asked a lot, but doesn't really have a concrete answer. No one person is identical. People are shaped differently, and personal preference varies from one fan to the next.
What we CAN tell you is that we haven't reinvented the t-shirt wheel. We offer a wide variety of sizes for both Men and Women. Our 50% Polyester, 50% Cotton premium heathered tops are sewn with a finer yarn than most "standard" t-shirts (40 singles v.s. 20 singles), thus a lighter weight garment (4.4 oz) with a slightly more tailored cut. Our sizing does not stray from traditional spec's, although the fabric is a bit lighter, while offering a more contoured fit.
A size chart can be found on each product details page.