At some point in time (recently) my CUPS printing broke. Broke might not be quite the right word to use; it still worked, but everything was coming out really big. As with so many of these type of problems, it turned out to be something I’d introduced rather something Debian had broken.
The issue was that my resolution in CUPS was set to 300×300, whilst my xprint default resolution was set to 600×600, hence everything coming out doube-sized.
The Solution
Edit the following file:
/etc/Xprint/C/print/attributes/document
Look for the parameter:
*default-printer-resolution: 600
Change the value to 300.