Before we continue with the mat, we must acknowledge something important (and rather curious) about the frame. The frame is usually not the size it claims to be. Try this. Take a ready made 11″x14″ frame off the rack and measure the recess at the back. It’s this recess – what framers call the “rabbet” of the frame – that is supposed to be 11″x14″. You’ll find that it’s not. Not exactly anyway. It’s actually 11-1/8″ x 14-1/8″. That’s because whoever cut the frame included an “allowance” in the rabbet.