The half chest measurements published on this site relate to the garment, not the person. These are measured from a point about 2cm below the armhole (outside of garment). Measure a garment you love for comparison purposes; however please be aware that there are many variables such as fabric thickness and stretch which can affect the comparison. So use as a guide only, and obtain sample garments for accurate sizing.
Note also that not all styles have the same fit or measurements; some are designed more fitted than others. So a size XL in one style may have a different fit to an XL in another style. ‘Classic fit’ is reasonably generous sizing, while ‘fashion fit’ is slimmer.
Aurora women’s sizing is based on NZ/UK sizing. Note this is quite different to US sizing: