To set q’s console output to 80 columns wide and 24 rows high (console size), use \c:

q)\c 80 24

You can also use the $LINES and $COLUMNS environment variables to have q start up automatically with your preferred settings:

$ export LINES=40
$ export COLUMNS=120
$ q
KDB+ 2.7 2011.02.16 Copyright © 1993-2011 Kx Systems
40 120

To adjust the amount of output when access a q server via a web browser, see http page size (\C)

Lastly, you may be interested in .Q.s and .Q.s1