When I first started quilting and Simply quilts was still on TV, I watched a show that asked that same question. She said that a good rule of thumb is at least 3 yrds. So have been buying at least 3 yrds. Sometimes if I really like it or it is a little over at the end of the bolt I will buy a little more. But to just put in stash because I like it but have no project in mind, 3. Hope this helps.
Rita