In the images I have models with different sized busts and band sizes to help you see how this style fits. Also some ladies the sizing wasn't quite right - so I offer my recommendations for these.
Jasmin our 1st model (wearing the Penny in natural with lace), is a 10G and here is wearing the size Medium in Penny Bralette. This size is a little big for her, as there is less support in the cups at the front and the band is loose at the back. Jasmin should have the size Small in the Penny, to get a firmer fit in the cups and more support from the band.
Georgia (wearing the black style Penny with mesh panels) is a 8G and wearing Penny in a XS. This is a great fit on her bust as the correct band helps support her bust size.
Martina (wearing the Natural with lace), is a 12D and is also wearing size M in our Penny Bralette. While this fits her well in the band, the cups in the Penny are too big for her and the style then comes up too far under her arms.
And lastly is here is Unjalung (in the black style Penny with mesh panels) is she is a 10G, and wearing a size Small in the Penny. This size fit her well in the band, and the cup.