When you enable Paper Size Auto Detect, the following paper sizes are detected automatically when they are loaded in the paper cassette.
A6, B6, A5, B5, A4, B4, A3
Similar paper sizes such as A4 and Letter may not be detected correctly. If Half letter, Letter, Legal, and 11×17 in. sizes are detected as A5, A4, B4, and A3 sizes, press the 
button and then set the correct size.
If the sizes cannot be automatically detected, press the button, disable the Paper Size Auto Detect feature, and then set the paper size that you loaded.