Sizing Approximate Bra Size: Small- 33-34 Medium- 35-36 Large- 37-38 X-Large 39-40 XX-Large 41-42 These are approximate. If you are in between sizes, we suggest you go down a size. Undercover Mama functions as an undershirt, keeping your back, sides and belly covered as you nurse. It has no straps and attaches directly to the outer flaps of any top-opening nursing bra. Undercover Mama remains attached while in use. You will feel like you are wearing a regular cami under you shirt, but when you need to nurse you still just have to undo the flap on your bra and Undercover Mama opens with it!Undercover Mama's generous length make them great to layer under your shirts and allow you to nurse comfortably.