For the 2 1/2" little squares, I've been using 4 1/8" squares cut on the diagonal twice (like an hourglass block) for the side triangles, and 2 3/8" cut on the diagonal for the corners. You need two of each square per block. All you have to trim are the little dog ears.
I hope this isn't stepping on any one's toes -- just giving another option for the block construction if you want it! :)