I have both 15.5" and 16.5" square Creative Grids rulers. I used the 15.5" one for the D9P. I'll be using the 16.5" one soon with the Storm at Sea class I'm taking next mo. The blocks are 16". The "Turning Twenty...Again" patterns have 16" blocks as well. I use the 16.5" along with my 6.5 x 24" ruler for cutting fabric. They're both handy rulers to have. JCY