Just a couple of screenshots of Fluttershy, both from My Little Pony and Equestria Girls.
For a while I've been wondering about the correct and exact size and height between the Equestrian ponies and the Canterlot High humans, until I compared the size of the Angel Bunnies from each Fluttershy and it seems just about right. A pretty simple method and it has probably been established already, but I thought I'd just throw it out there anyway.
Note: The original idea behind this is not mine. I orignally found it here, so credit goes to that person who thought of it first.