The twister is fun, but does use a fair bit of fabric! You will need to cut 5" squares, I don't think 4" will make it. If your starting piece is 9 X7 squares, you position the ruler at the block intersections, so you will wind up with 8 X6 twister blocks. Since the ruler is 3.5" it will finish at 3". You will get 8X3" by 6 x3" or 24" X 18" finished size plus whatever borders you add.
I think that's why they came out with the mini twister tool. You sew together the pieces left over from the first cut and cut mini squares.