At local stores sometimes you can buy as little as an eighth-yard (1/8 yard), so not very much. In person you never have to buy more than a quarter-yard, or a fat quarter, which is a pretty convenient amount.

Online I did have to buy usually at least a half-yard, but the lovely fabrics I found online were usually worth it.

I did end up with a whole yard of the cards fabric, but that's because it was on sale, and I had to buy the whole thing. But it was only like $3.50 or something. Still, not sure what else I'd use it for *g*