Function: frame-height

Return number of lines available for display on FRAME.
If FRAME is omitted, describe the currently selected frame.
Exactly what is included in the return value depends on the
window-system and toolkit in use - see `frame-pixel-height' for
more details. The lines are in units of the default font height.

The result is roughly related to the frame pixel height via
height in pixels = height in lines * `frame-char-height'.
However, this is only approximate, and is complicated e.g. by the
fact that individual window lines and menu bar lines can have differing font heights.