well, here is my own formula: If I think it would make a good outer border? I buy three yards for a full size/queen bed. That's bc I like to cut my borders on one piece with the selvedge. It doesn't stretch as much and if I didn't pay that much to the direction of the print, this saves me from finding out, later that crossgrain might not look as good.
I also have some left to use in center or on the backing or other borders.
If it's going to be for a lap, I buy two yards.
If it's going to be with other fabrics in the center, depending on how much I like it, I will buy one to two yards.
I'd much rather have too much than not enough.
Occasionally I buy for blocks to mail or a very small project. Then I buy at least 1/4 - 1/3 yard. I have on occasion liked these pieces so much, I wish I had gotten more. Can't have it all, can we???
FRom the looks of my stash, I must be trying, lol. :wink:
BTW: I lean towards samplers and quilts with lots of different colors or fabrics. If I was making a quilt with mostly the same blocks, I would probably buy at least 4 yards for the center background, or MAIN fabric.
Maybe even more, depending on size.
The average queen size quilt needs 8 1/2 yards for the backing, so, the front, center needs 4-6, maybe more for a repeat block, esp. if you also put it in outer border or binding.