I buy 1 yard pieces. If its a really great versitile fabric I buy 2 yards. This is enough for a small project, or scrappy projects, and have plenty for your stash. I would not buy large amounts because our taste in fabric changes over time.
Plus they are always making new fabrics every year. Add to your stash a little every year, instead of trying to build a stash in one-two years.

If I have the funds, I buy at least 3 yards of a matching medley of 3-4 fabrics, and then 6 yards of one for future backings. Fabric prices are going up, so if the sale is good, stock up. Good quality white goods, I buy at least 6 yards as it always comes in handy. I also carry with me in a little baggie, project samples stapled together so I can add a medley to a proposed project.

As a general rule, I buy 3 yards. I don't like to piece my borders so 3 yards is plenty to cut parallel to the selvage (straight of grain) for my quilts as I rarely have a need for a border longer than 108". Three yards also seems to be enough if I want to use as a background.

Depends on the design and color and price but I would say about 5 to 6 yards.

For some reason I buy an extra 1/2 yd. If I want to buy 3 yards, I make it 3 1/2 yards, always have a little left then for scrappy or other small amounts needed. If the price is good I would buy at least 3 1/2 - 4 1/2 yards. Good luck

I mostly buy fabric with something in mind for someone. I usually buy 3yds

2 to 5 yards

I buy three unless I really love it then I buy five. When I love one I use it in more than one project.

same for me too

Sounds like I do what some of the others on this thread. Of course I asked my mom what she does as well. 3 yards if I love it. 5-6 yards to use as backing. At some of the shows I can get to, several of the vendors have group "batches": 1/2 yds, 1 yd, and 3 yds. I love FQs but as I go along on my quilt journey I find more success with buying FQ bundles instead of singles.