This is an oversized boxy fit.
Rae wears size M and is a 10-12 on top
Rough guide - XS6-8 S8-10 M10-12 L12-14 XL14-16 however this is a boxy fit so you can size down or up depending on the fit you want. See measurements below.
Measured flat in cm across chest (1cm below armpit). XS51 S53.5 M57 L61 XL63.5
Body Length XS62 S63 M64 L65 XL66