If I had a fabric shop, I would make sure that the first cut of the fabric is on grain by tearing the first edge. Then I would measure whatever the customer wanted and just make it a little bit more--in case. When I buy my fabric, I always add 1/4 inch and sometimes 1/2 inch if I'm not going to make the quilt right away. I don't want to take a chance and not be able to get what I need if I make a wrong cut or if by chance the pattern in wrong.