window-normal-size

window-normal-size is a built-in function in `C source code'.

(window-normal-size &optional WINDOW HORIZONTAL)

Return the normal height of window WINDOW.
WINDOW must be a valid window and defaults to the selected one.
If HORIZONTAL is non-nil, return the normal width of WINDOW.

The normal height of a frame's root window or a window that is
horizontally combined (a window that has a left or right sibling) is
1.0. The normal height of a window that is vertically combined (has a
sibling above or below) is the fraction of the window's height with
respect to its parent. The sum of the normal heights of all windows in a
vertical combination equals 1.0.

Similarly, the normal width of a frame's root window or a window that is
vertically combined equals 1.0. The normal width of a window that is
horizontally combined is the fraction of the window's width with respect
to its parent. The sum of the normal widths of all windows in a
horizontal combination equals 1.0.

The normal sizes of windows are used to restore the proportional sizes
of windows after they have been shrunk to their minimum sizes; for
example when a frame is temporarily made very small and afterwards gets
re-enlarged to its previous size.