ps-line-number-font-size

ps-line-number-font-size is a variable defined in `ps-print.el'.
Its value is

6

Documentation:
Font size, in points, for line number, when generating PostScript.
Either a float or a cons of floats (LANDSCAPE-SIZE . PORTRAIT-SIZE).

You can customize this variable.

This variable was introduced, or its default value was changed, in version 20 of Emacs.