For these DIY fabric coasters, all you need to start is a scrap of fabric with straight edges for the center of each coaster.
It can be any shape, a triangle, a square, a hexagon, a trapezoid, anything with straight sides. You can decide how big you want your starting scraps to be I think mine were between 1″ and 2.5″ wide all around in general.
Find a scrap that is slightly longer than one straight edge of your first scrap and place it right sides together and sew in place along the raw edge with a 1/4″ seam allowance.