I thought that these would be fun workout t-shirts so I bought one for me and for my husband. I followed the directions for measuring size against a well-fitting t-shirt and placed the order. Upon arrival, both shirts were too small and so we returned them for exchange at our expense (as an aside, the exchange site address noted on the invoice is not correct). The next size up only barely fit. I made the mistake of taking the shirt to wear for my workout, but realized that it is really too tight to be flattering. It looks as though the actual size I should have ordered is two sizes larger than the original size. My husband's shirt is similarly only barely large enough.
The cotton is comfortable and the design is as charming as pictured -- but given the sizing discrepancy, I am unhappy with myself for making this purchase. Unless you want a very close-fitting shirt, I would be cautious in sizing.