that's what i would do. sew the 2 pieces together, face to face, along each edge to create a tube.
press so that the seams are one right above the other. you should have pressed creases in the center of both lengths. open the fabric up and cut along ONE of the crease marks. you'll have a wide band in the center and a narrow band on each side. trim off what you don't need and call it stash. use part for a label.
it's not a good idea to make a backing with one seam down the middle. it doesn't hold up as well. try for two seams up and down or across.

Tearing is the only way to be sure you are getting a straight edge and if the seam is not centered, who is going to notice?
I use the folding cutting boards for large pieces of fabric. One just fits on a twin bed, two are as big as a queen size quilt. I shove our beds together and have a nice working surface. If you are fortunate to have floor space that big,lay out the backing to measure and cut or tear.

Carol J.

I realize you already have this fabric, but for those that don't and might like to know-- you can get quilt backing fabric in 108" ($5.99 per yd) and natural and white sheeting 118" ($3.99 yd)
widths at http://www.marshalldrygoods.com/
Meg

What I would do is cut it into equal thirds instead of two pieces, sew together, measure again, lay under quilt, measure again, baste, check that everything is ok with it, flip over, see what it looks like. If you don't like it flip back over and start again. Before I would cut anything extra off, I would be reallly sure of my measurements and placing.

I also tear long strips of fabric...but make sure to tear you a small strip off the edge to get it all straight before doing your "big" tear. I usually will nip about 1 1/2" from the side, tear that strip off, and then tear the main strips I am after. Helps to make sure the edge is straight before tearing it.

I do what my mom, a seamtress, also does. I crawl around on the floor with my cardboard cutting/measuring board that is 5 or 6 feet long, position my fabric on the correct lines and cut with scissors. that's why leaving 3-4 inches on each side of the backing is so helpful - if I get a _little_ off - it doesn't matter.

Thanks to you for the Marshalls online connection. They have the most selection of backing fabric selection that I have found.
I also do the tube method (if I cannot find whole cloth backing) because I some times use the back of the quilt as a whole cloth quilt (this means that I have 2 sides of the quilt to decorate the bed.) My children like this because the boys like the solid and the girls like the patchwork side.

Why not get 2 looks for 1 effort. I want the back side to be as beautiful as the front and whole cloth quilts are beginning to show up.
Gail

I would tear it also. That is one sure way to get a straight edge.

The owners of a couple of LQ here let customers come in and use their cutting tables free, if there is not a class going on. You might ask. All they can say is no. I took one quilt in and basted it on their table. We live in a micro apt and there is no room to work with a big quilt.

Thank you so much for the awesome site for fabric!!! I just spent about 20 min looking at all the stuff they have!!!! WOW! How is their shipping & handling price? :-D