OK, I know that size is an issue with Doublju shirts so I hope this will help. I ordered this shirt and a Fruit of The Loom shirt (add-on item) in the same order. With this shirt I followed the instructions to order the Korean Medium in order to get a US Small. I ordered the Fuit of The Loom shirt in Small since they are already sized for the US market. So... in theory, both shirts should have been the same size, SMALL. When laid flat, measured at the waist, this shirt measures 16", the FTL measures 18 1/2". So that is a diameter of 32" compared to 37". A full 5" difference.  Clearly I should have ordered a Large which they would have considered a US Medium. At best, their Medium is somewhere between XS and S, and I'm guessing their Large is between S and M, no pun intended.

Otherwise it is a nice shirt, with good color choices. Not any kind of special fabric, but well made. Just a bit tight even for a small.