number of lines and columns of your terminal

$ tput lines
22
$ tput cols
165

Of course, the values depend on your own settings.

I found it in the script snowjob.sh, which adds snowflakes to your terminal. Really cool.

Related animated short film: Operation White Widow (2011).

Update
In Nim, there are functions for these in the module terminal. See terminalWidth and terminalHeight.