The VTee is a slightly generous size. The small will fit someone who is between an 8 and a 10 and so-on. The shorts are pretty much on size, the XS will fit a size 6-8, the S will fit someone who is an 8-10 and so-on. Please do contact me if you need any exact dimensions.
Will fit a UK size 6-8 or a US size 4-6
Will fit a UK size 8-10 0r a US size 6-8
Will fit a UK size 10-12 or a US size 8-10
Will fit a UK size 12-14 or a US size 10-12