This serves as a general guide only

Crop Tops
XS: AUS 6
S: AUS 8
M: AUS 8-10
L: AUS 12-14

Choice of top size also depends on level of support required and personal comfort level. Ladies who prefer a firm fit generally go for smaller size.

Leggings

XS: AUS 6-8
S: AUS 8-10
M: AUS 10-12
L: AUS 12-14

If in between sizes or unsure, go for the smaller size. These leggings are of compression fabric and are designed to be worn fitted. They hold and tuck you in all the right places. It also moulds to your body after a few wears and washes, giving you the most comfortable feel and fit.
We also go with this chat as a general international guide: