One of the many advantages of paper piecing is how easy it is to make blocks whatever size you need, simply with the help of any photocopier or nowadays, most home printers. When you are ready to copy or print the block pattern to create your foundations, input the correct resizing percentage into the machine: percentages larger than 100 will enlarge the pattern (make it bigger); percentages smaller than 100 will reduce the pattern (make it smaller).
It’s easy to figure out the correct resizing percentage to put into the copier by using this formula:
Let’s take an easy example — you have a 6″ (finished size) block pattern, but a 12″ (finished size) block is needed for your project. Intuitively you know the size must be doubled, or enlarged 200%. Using our formula, you can see that:
12 inches (desired size) / 6 inches (current size) X 100 = 200%
This formula works for any measurement units, as long as they are the same units (inches, centimeters, yards, etc.) for the before and after measurement.
Now we’ll take a different, and not so intuitively obvious, example: you need to reduce your 12″ block to 8-1/2″ (finished size). Again, using our formula:
8.5 inches (desired size) / 12 inches (current size) X 100 = 70.83%
Most copiers or printers only allow percentages of whole numbers. So round up to 71%, which is sufficiently accurate for typical quilt block sizes.
With quilt patterns, remember to always work with finished size block measurements (i.e. the measurement without the outer seam allowance) when figuring out your resizing percentages. Using a block size that includes seam allowances will lead to inaccuracies when resizing, because you would also be proportionately enlarging or reducing the seam allowance when, in fact, the standard seam allowance is 1/4″ regardless of the size of the block.
This is the reason that many quilt designers, myself included, don’t include printed seam allowances on their paper piecing patterns, so as not to confuse quilters when resizing blocks. The seam allowance on a resized block would no longer be a true 1/4″.
If you’re handy with Excel or another spreadsheet program, you can create a nifty little resizing tool to figure out percentages automatically from any (finished) block size to any other block size. Here’s two Excel versions I’ve created for you. The first is for converting inches to inches; the second converts inches to centimeters:
For a Microsoft Excel file which will convert both square and rectangular blocks (sized in INCHES) to whatever size you need in INCHES, click here.
For a Microsoft Excel file which will convert both square and rectangular blocks (sized in INCHES) to whatever size you need in CENTIMETERS, click here.