My best solution would be to measure with a yardstick (mine is on the wall in sewing room) two yard lengths, nip with scissors, then rip. 2 yards is a nice manageable size to work with. I would zig zag the edges before washing just to avoid all the string tangles. Good luck on the quilt. Please post as you go we would all love to see your progress.
(I got my yardstick at Walmart for $3 )