depends on how many strips were in your jelly roll- they vary- some contain 20 strips, some 40 or more- a jelly roll strip is 2 1/2" x width of fabric (generally about 42" long) so if you have 20 strips and you sew them together you will have a piece of pieced fabric that measures about 40" x 42" (or a bit less if you cut off the salvages on the ends of each strip) if you have a 40 strip jelly roll and sew them all together side by side it will measure about 80" x 42"...different collections have different amounts of fabrics - usually a jelly roll bundle will tell you how many strips are included....the only (common denomenator ) is the length.