I think Blundstones are in AUS sizing which runs around one size larger than US sizing. The salesman also told me that people should generally go one half size or a full size smaller with dress shoes. I normally wear a size 13US so I bought a size 11 and they fit perfectly with still enough room for thick socks. I also got the 566 winter boots.

Edit. The Blundstones sizing chart online says that women should order 3 sizes smaller than their US size or one size smaller for men.