This top is a tag size US 10, made by Burberry London.  It is in excellent condition with no flaws to note.

You can measure a garment that fits you well and compare it to the measurements of the item I have for sale.    
 
Manufacturer size tags often do not match the actual measurements.

These are the actual garment measurements.  They are approximate (to the nearest 1/2 inch) and taken from edge to edge while the item is laying flat:

Pit to pit:  21
Back collar seam to bottom hem: 24.5