This is really a mathematical question. Assuming you have 40 2.5" strips in each roll.
You will have a quilt either 106 wide by 64 long, or 53 wide by 128 long.
When you do a jelly roll race you are continuously dividing the loooooong strip in half. If you start out with 2 jelly rolls it is approximately 3440 inches long.
You sew it in half once, 1720 x 4.5
Sew in half 2 times, 860 x 8.5
3 times, 430 x 16.5
4 times 215 x 32.5
5 times 107.5 x 64.5 (this is where you normally stop - jelly roll race sewn with .25" seams is 64.5" long)
If you go for one more 53.75 x 128.5
If you want a longer quilt, but still sort of square, you have to use wider strips.
I think I once used 45 - 3" strips to get a quilt 80" long and 60" wide.
Understand, I am a math person and love to figure these things out!!!
Good luck!
Ann
Last edited by krafty14; 08-13-2015 at 02:48 PM.