I have a Fons and Porter Half and Quarter ruler. To be sure I knew what I was talking about I just went to my sewing room and took two 3" squares (because they were handy) and using the ruler made a half square triangle which measures 3 inches square when finished!! The only thing is.....the ruler is just marked up to 4 inches, but it would be very easy to figure the 5 inch line and mark it with a piece of painter's tape, etc. I use this ruler a lot. You can take a 2 1/2 inch jelly roll and using this ruler make 2 1/2" HST.