I'm just wondering if there is a website that I can go to that gives the measurements for the different sizes in the boots?

I got some Medium hinds for my mare as she wears medium all the way around in the Professionals Choice. And the Classic's seem a little big to me. I'm not worried about returning these or anything as I'll keep them for my other horse, I just want to make sure I got the correct size and if they are not right I want to make sure I get the right one's. 

you can call them

www.equibrand.com

They are great to work with.