Mavericks - terminal change default printer paper size I've been using the following terminal command to set the current default printer paper size to a custom paper size  

defaults write com.apple.print.PrintingPrefs DefaultPaperID -string 154x216


Unfortunately looking in preferences panel this is not setting the paper size, please does anyone know where this default paper is now set in Mavericks
The setting in System Preferences changes the DefaultPaperID key in ~/Library/Preferences/org.cups.PrintingPrefs.plist. Try to change that key instead:

defaults write org.cups.PrintingPrefs DefaultPaperID 154x216


Quit and reopen applications to apply the changes. 

defaults read com.apple.print.custompapers shows the IDs of custom paper sizes.