Quilters ask me this question more often than any other:
“How much backing do I need to buy if my quilt is size X?”
There are a few ways to calculate this depending on the width of the fabric you’re buying. Most machine quilters will require at least 4” extra fabric in each direction for the quilting process, I will work that into my figures. I am also going off standard sizes for quilts: king, queen, full etc. So, if your quilt falls outside those standards, recalculating would be wise ;)
I love using minky fabric for the backs of my quilts; it typically comes 60” wide. I’ll give you the yardage needed for that, for the standard 44” wide goods, and the extra wide backing fabric that typically comes in 108” wide goods.
I don’t prewash my backings unless the rest of the fabric has been prewashed. You can lose quite a few inches by prewashing backing fabric especially if it is the extra wide backing goods. So if you are going to prewash, be sure to measure again after it’s been dried!
I've compiled this handy guide to help you select the perfect backing for your quilt. Download it, print it, and post it in your sewing room for quick reference.
Hopefully this helps!