Hi,
See Boo's note on Scaling patterns. This is a copy of it.
Donna, although figuring additional yardage may seem complicated it really isn't. It is just a matter of reducing the task to it's basic elements, which are the size and number of strips needed. Each pattern will list cutting instructions for the yardage requirements to accomplish the size of the quilt as stated. If you wish to enlarge a quilt, lets say by a row of 6 blocks, figure how much fabric you will need for those additional blocks. The safest method would be to consider all fabric to be 42"wide. Okay are you with me so far? You know that math is coming, but don't zone out on me. This is simple, no quantum physics involved. Grab a calcualtor. If you need additional 6" squares, you will first need to know how many times 6 goes into 42". See told you not hard, so now how many 6" strips you need to cut would be 1 strip for every 7 squares. This is how you would figure additional yardage. It never hurts to buy extra, that is how a stash is built. Before you know it, you will have enough to play a new game called Scrap Quilts.
Boo
Hope that helps. Right now the original message is on page 3.
Would love to see a pic when you are finished.