You can make them any size you want. Just think about what size you want your quilt to be. Queen is around 90" X 108." If you wanted to use a layer cake (10" squares), they would make a 9" finished HST. 90" divided by 9" is 10 squares. 108" divided by 9" is 12 squares. So without borders, you would need 9 X 12 = 108 HSTs.
What size squares to you want?