You find the perfect quilt pattern except you wish it was a different size. What do you do? Adjusting the size of a pattern isn't difficult. It doesn't take calculus. But there is a trick.
Suppose you need to make a baby quilt and you like this cute nine patch. However, the pattern calls for you to use 2 ½" and 6 ½" squares and the finished block size is 18". No matter how cute the baby is, there's no way you want to mess around with all those tiny squares. You decide you want to make it finish to be a 27" block cause, you know, bigger is better.
Make it Bigger!
First, determine how much you are increasing (or decreasing) the finished block. Take the bigger size and subtract the original size (in this case, 27" - 18" = 9") then divide this by the original size (9"/18" = 50%). In other words, your new block is 50% bigger than your original block.
Now you need to adjust each piece.
1. Remove the seam allowance to get the finished size of the piece. In this example, the small squares are 2 ½" with a ¼" seam allowance. Remove the seam allowance from both sides to get 2" finished.
2. Calculate the finished size of the square in the bigger quilt by adding the percentage increase. In this one, 2" + 50% = 2" + 1" = 3".
3. Add the seam allowance back to your new, bigger square. 3" + ½" = 3 ½"
Now, let's do the 6 ½" square:
- Remove seam allowance = 6 ½" - ½" = 6"
- Increase size = 6" + 50% = 6" + 3" = 9"
- Add seam allowance = 9" + ½" = 9 ½"
Tips:
This same technique will work for other shapes, just adjust each dimension.
If you want to make the pattern smaller, you'll just subtract the percentage decrease.
Okay, enough math, you've got sewing to do! Have fun!