-I cut my binding 2.5" wide. I like it to be a bit wider, more of a part of the "frame". So, many times, I will stitch 1/4" from the edge, and it gives me more on the front side of the quilt. If it doesn't matter, I might sew 3/8" from the edge, as I did here.
I figure the length by: inches around the quilt, divided by 40, which is the width of fabric, 40 is a good average and easy to figure, sometimes it is 40", sometimes it is 42". I don't like to cut it close. That is the number of strips you will need. I round up to the next number: 7.4=8. If it is too close to that number, I add one. Say 7.9, doesn't give me enough for much fudge room, so I would cut 9, which is plenty. I save all of my extra binding and use it on my scrap quilts. In this tutorial, I have sewn the binding to the back, to wrap around to the front, and I sew it down with a decorative stitch. I also sew it to the front and wrap it to the back if I am going to sew it down by hand.
Sew binding strips together, end to end on the diagonal. (It is on the diag. usually so there isn't so much bulk when you fold it and sew it to the quilt.) I move the top piece over, so it is easier to see the bottom corner. One thing I do is lay out all the strips in a pile on my lap, take the first layer off, and sew the next 2 layers together, etc. and then I am sure not to sew a "loop" by accidentally sewing that first end of the strip to another one. But, do it once, and you probably won't do it again...!
Start to sew the binding on the quilt raw edge to raw edge. Never start at a corner, or even near the corner. I usually start about in the middle of one side. Leave a tail that does not get sewn down, start sewing about 8" from the end.
When you get to the corner, stop sewing 1/4" (or whatever distance you are sewing your binding at) turn your quilt to sew down the next side, but sew OFF the quilt backwards.
Now you have gone all the way around, and ended up back at the beginning. This is the tricky part, until you get used to it! Don't sew all the way, stop about 8 inches or more from where you started. Overlap binding at the started end. You will cut the binding at the overlap, (white dot for mine) the same distance that you cut the width of the binding. In my case, it was 2.5". (Hope this makes sense...)
Open binding, and pin the ends together, like you did with the other pieces in the beginning, except you put it exactly at the end, because this is your final measurement. Here you might want to use pins, as it is harder to muscle the binding now. This why you leave it unstitched at the end. If you feel like you don't have enough room, you can rip out some stitches either at the end or beginning to help.
Once you finish sewing the ends, DOUBLE CHECK to make sure that the binding fits, and that you have sewn it correctly and haven't twisted the ends before cutting the excess. Then, cut the excess and finish sewing down the binding, back stitching over both ends.
Iron the binding flat and the seam open all the way around. Roll the binding to the front side of the quilt, and stitch, (covering the back stitching) and stitch with desired decorative stitch. I just used a multi-stitch zig-zag.
When you get to the corner, make sure you get a nice fold, and then fold it down and then back up. You will know if it is right, if the points match when you fold it back up.
I stitch the corner down, even tho it doesn't look great all the time, but I have had them come unfolded, and then they don't look so great either.
Of course if you want to do this part by hand, that is o.k. too. I figure most of my quilts are going to be used to death, so function is more important than looks. I try to do it as nicely as possible, but doesn't always work the way we plan!