When a piece of fabric jumps into my arms, and I have to have it, I buy at least 3 yards, that should usually be enough for a quilt; however, when it comes to background fabrics, white, beige, grey, black, etc. I tend to buy 6 yds. if I can so that I won't run out. If it's a really good deal, I've been known to buy 6-9 yds., which would give me enough for a backing. I once ran into a fantastic sale at a LQS, who was selling from bolts of fabric that had been on their shelves, they were just making room, in that case, and I was able to buy it I bought 3 or 4 pieces of 6-9 yds. One background fabric I bought decided that it wanted to be on the front of the quilt, so I was glad I had purchased it as using it for the focus fabric in a Jacob's Ladder quilt, my church made about $500 from that raffle quilt. I have to be a little more frugal now that we are retired on SS, however, I am so glad I have my stash so I can continue to make quilts, buying usually fabrics for backgrounds and backings when I've run out of a particular color.