20-1/2 is my largest. I don't use it often but am so glad to have it when I need it. I use the 12-1/2 the most. Also lots of use for the 6" and the 6-1/2". I had a 3x18 ruler that broke in half and I loved the 3x9 size til I wore it out. I use the 6x24 lots too.