Had a similar situation not long ago at my LQS. I had my top with me, no borders planned, just looking for backing. New employee punches numbers into the fabric calculator, tells me yardage. I always buy extra from 1/4 to 1/2 yard. Bought an extra 1/2 yard and was still quite a bit short. Had to go back and buy more. New employee was not there at the time, everyone else busy. Needed the fabric anyhow so just bought the fabric and left. I'll be going by MY calcuations next time.