Originally Posted by
NanaCsews2
I would simplify everything and cut the "solid" squares 3 1/2", and for the HST's cut them to measure 4 1/2". Sew the HST's, and trim down to 3 1/2, as your solid squares would be. All squares would then sew out to be a finished 3" size.
This is the correct answer. If you want your squares to be 3 in. finished, which is what the OP stated, you need the squares to be 3.5 inches. And 4.5 is a good size for the HSTs.
Do not cut three inch strips. All the HSTs need to be one inch larger. If you want to start with strips, cut some three and one half, and the others four and one half.