First of all, I have to say that it took me a couple of orders with free shipping each way, to figure my sizing out on this blazer.  For reference, I am 5' 8" and weigh an athletic 143.  My bust is 36", waist is 29" and hips are 38".  I normally wear a 6 or sometimes an 8 in U.S. sizing.  That is a Small or Medium.

Having read loads of reviews, I ordered this first in both a Medium and Large.  The large worked, but was maybe a bit more fitted then I wanted (it was VERY fitted).  I like a blazer with some shape to it, but I don't want my bra lines to show right through it.  So I next ordered it in XL.  This was perfect for me.  And the larger size is a bit longer too, which is nice for me because I'm fairly tall.

It's worth commenting here that an item of clothing at this price is not going to be of Designer quality...so be sure your expectations are in the right place.  The blazers are quite nice though, flattering and they are unlined and stretchy.  I show dogs and need to look nice, but also need to be comfortable and able to move all around, so the stretchy fabric is perfect for me.  You can dress these up...or dress them down with jeans.  VERY cute.

After finally figuring out my size, I went ahead and ordered a few more in other colors.  This is a sharp looking blazer and for the right events, it's ideal.