As Grannie Annie implies, there is no standard number of strips or squares in a jelly roll, charm pack or layer cake, so you really can't give a yardage on a 'jelly roll'. Some have 20, some 40 or more. I know I've seen the reverse, how many charms can you cut from a yard of fabric...
http://quiltville.blogspot.com/2005/...s-in-yard.html