Marie, depending on your own personal measurements, the BOM will finish to approximately 85" square. That means that two lengths of fabric (I would get 5 yards) will be enough for the backing IF the fabric measures more than 44" wide, but you won't have much extra on the sides. :shock:
That will allow for a seam down the middle, and trimming off the selvage edges, but not much for matching the pattern at the seam.
You might want to consider making a pieced back and making it large enough to be more generous around the edges!
A huge sawtooth star on the back would be really cool!
It's Not What You Gather, But What You Scatter
That Tells What Kind Of Life You Have Lived !