Originally Posted by KarenK
Work with finished block sizes, then add the 1/4" seam allowance.
(New block size) divided by (current block size) times 100 = % to enlarge
12" divided by 4.5" times 100 = 266.66666666 or 267%
You can use your own printer ( it gives you the directions) to make a four page pattern that you can tape together.
But be aware distortion can happen. Make two at 90* difference, and compare the measurements by putting one
over the top of the other, taping them to a window, and seeing if they match. If they don't ( worst case ) put on another piece of paper and draw the lines that fit the 12.5 block. It sounds much harder than it really is.