Apparently not all fat quarters are made equal, so I had to trim mine to the same size, 16.5" x 18". This isn't rocket-science, to be sure. Just a reminder how easy it can be to make a relatively simple quilt back at a moment's notice. And considering the easiest quilt backing of all time (to me) is one made from one length of fabric, this must surely be the second.
Using 12 fat quarters, this quilt back measured 53" x 64.5".