Lovely quilt. It seems to be double-bed size, which is about 54" wide. I'd suggest cutting 1-1/2" strips [ 1" finished] and 2-1/2" [2"fin] for the center square. This should give you a 10-1/2" block and with 2" sashing, 4 blocks will cover the top of the bed. Your sashing would then be cut 2-1/2".
If you prefer to make your quilt larger, then by all means cut the strips wider.
Cutting 2" strips should make a 15" block,
and 2.5" strips will make a 20"block.
Hope I have helped.