Of course this all depends on how a store sizes their clothing. At Lane Bryant, I'm an 18 or 20. In other stores, I could be anywhere from an 18 to 24 or 1x to 3x. It depends on who is making the clothing and the cut, fit, and style.
I try on EVERYTHING I buy. I prefer to shop in stores, but occasionally will buy online.
Will let you all know how those tanks I bought from SWAK fit. Crossing my fingers!