Keep in mind that buying leather is not like buying fabric. You're not buying buy the yard, or even by the square foot. You're buying by the whole hide. Since animals come in different sizes, sellers use rough square foot measurements simply for the purpose of pricing. Depending on how the hide was dressed, some of the square footage isn't really of a usable size/shape other than for making laces.
My advice... always buy the largest hide you can. You'll always use the extra for something. Also, generally speaking, the larger the hide the thicker it is which helps when making moccasins.