Model is wearing is wearing a size S.
Top size depends on the style and look you like.
Example: You may be a C/D cup which is normally a size M, but desire less coverage- a size S would suit this look.
If you have a wide back please size up.
For Baby Pink/Silver 2 piece & Electric Blue one piece: Sizes run small meaning: SMALL is really a XS, MEDIUM is really SMALL, LARGE is MEDIUM, and so on.
For Black & Red one piece: Sizes run true to size: SMALL is S, MEDIUM is M, LARGE is L, and so on.