Hi Sue, if I can remember back to when I made mine, each strip set, the width of the fabric makes 2 completed 12" blocks if you cut them into 9 1/2 "squares, so to make the quilt shown you will need 5 strip sets to make a quilt roughly 36" by 36" then add borders. I made 6 strip sets and made it 3 blocks by 4 blocks and added borders and ended up with a nice lap sized quilt. To make it bigger just add more blocks, so a 4 blocks by 5 blocks quilt will need 10 strip sets.
If you want to make the 18" block I think you will only get 1 block per strip set.
I hope this helps :?