You need one for the center, one for the "middle layer", cut in cross from corners, and two for the corners, cut into triangles from corner to corner. Then sew. Cleaver idea and more interesting than the traditional bandanna quilts.
Great idea for a modular knit blanket. One simple shape makes a great quilt. Sidewalk Quilt by Pippa, an original design. Pattern available on her website and a similar version for sale in her Etsy shop.