Assuming a usable length of 40" and 2" finished width, one strip gives you 80 square inches. If you want your quilt to be 60x80, for instance, that is 4800 square inches, and 4800/80=60 strips. For a quilt that is 60x60, 3600/80=45 strips. That's for a quilt that's made with jelly rolls, not necessarily for a jelly roll race quilt. The difference is in the construction, since for a jelly roll race you start with one large strip and start halving it in one dimension, doubling in the other. The jelly roll race quilt is more of a novelty IMHO, lots of fun, but harder to construct because of the long twisting chain of fabric and harder to control because of the way the size evolves.