Using 2" wide binding...questions...
 

I made a runner and I only have enough binding fabric to make the binding 2" wide. I've never done binding this narrow, although I have done 2.25" so it's probably not too much of a difference. Anyway, if you use this size, what seam allowance do you like to use?

I like narrow bindings. Although I don’t actually measure my seam allowance I’m guessing my seam allowance is about a scant quarter. I use thin batting in table runners and zigzag around the edges before adding the binding.

I use 2" all the time (because I also run into that problem of not quite enough fabric). I sew it on using a bit skimpier of a seam.

I probably only sew it about 1/16th inch less, so it's right on the side of my foot instead of a bit over. I sew a few inches and then turn it to see if it's going to work, and adjust as needed. I don't unsew the "bad" part (if there is one) from starting wrong until I get all the way around and back to the beginning.

I've done 2" for many years and a
1/4" seam. I've been dabbling with a few modern quilts lately and I think they benefit from a slightly wider binding with 1/2" seam.

make a small sample from some scraps. The seam allowance depends somewhat on the thickness of the quilt.

Seam allowance would be dependent on the thickness of your batting.
You may still be using a 1/4".

Start with a long basting stitch and try it at 1/4".
Fold over as though ready to hand stitch, to check it it just covers the line of stitching.
If not, then go a bit narrower.
Or if it goes way past the stitch line, then make your seam allowance wider.

Once you have your seam width determined, be sure to stitch over the basting stitches.

Thanks everyone. I hadn't thought of a flanged binding. I might have some coordinating that would work. If not I'll definitely try a scrap or at least baste first. This might be something I continue to do for wall hangings too-I read that a lot of people like a narrow binding on them.

Some people do not press their binding. That may help when turning the binding to the other side.

If you use 2 1/2 in. binding and sew with a 1/4 inch seam, the binding will not be full when it is turned.
I trim the back and batt roughly to leave some extra before I sew on the binding. Then after the binding is sewn on with a 1/4 inch seam from the edge of the top, I use a ruler and cut the back and batt 3/8 of an inch from the sewing line. This give a full binding, especially if I turn it to the back and sew stitch-in-the-ditch from the front. The seam is always the correct width.