If I want to know how wide a window is, in terms of characters of a given
face, I can use #'window-max-chars-per-line (
https://www.gnu.org/software/emacs/manual/html_node/elisp/Window-Sizes.html#index-window_002dmax_002dchars_002dper_002dline
).

But if I want to know how tall a window is in terms of characters of a
given face, I don't think there's a built-in method to do so. At least, I
can't seem to find it.

So I wrote one. This would be nice to get into Emacs if I haven't missed
any existing functionality. My code :

(defun zck--window-max-lines-per-window (face &optional window)
  "Calculate how many lines of text with face FACE can fit in WINDOW."
  (truncate (window-body-height window t)
            (window-font-height window face)))