Fashion Dollars and Sense

I know they have to be 10 heads but do they have to be a certain amount of inches tall to be good enough for fashion schools? I want to make a portfolio and I like to draw my figures about 9″ or 10 ” tall, but is that good enough? Do I need them to be afew inches taller? Or does it not even matter because they already have the right proportions? Please help me… ^_^ give as much info as you can, thanks soooo much!