dpi and inches do not match and will not change

I am trying to create an artboard that is 3600px by 3600px at 300dpi.  I have all the settings correct.  However, when I use the ruler, the px is correct, but the inches are 48, not 12 like I expected.  I also checked under Effect>Document Raster Effects Settings.  This is also set to 300dpi.  What is going on and how do I change it?  It acts like no matter what I set it to, the artboard is only going to open as 72dpi.