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Editorial Team
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Asked: 2026-06-12T23:55:36+00:00

I’m trying to write a function that does something based on Emacs’s current window

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I’m trying to write a function that does something based on Emacs’s current window width. The problem is, Emacs is confused about how wide a column is. It seems to be basing its calculations on the original font size and not my custom set one. Here is a screenshot to illustrate:

Screenshoot illustrating the problem

It seems to work correctly when I remove my custom font setting, so I think it must be not updating how big it thinks a column is after switching to a new font.

Here’s the relevant part of my visual config:

(setq default-frame-alist
  '(
    (font . "-apple-Ubuntu_Mono-medium-normal-normal-*-17-*-*-*-p-0-iso10646-1")
    (width . 130)
    (height . 45)))

(obviously the frame was resized from my defaults in the picture, but this is where my font gets set so it seems relevant)

And here’s the function I used to determine the computed current width:

(defun get-window-size ()
  (interactive)
  (message "The width is %d." (window-body-width)))

According to the docs, the window-body-width function should return just the editing area, so any discrepancy between column number and total frame size should be eliminated…

How do I make Emacs update its understanding of column width after changing font?

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1 Answer

  1. Editorial Team

    The “line&column” position indicated is based on the number of characters (tho some characters can count as 2 columns or more, TAB being a common example) rather than based on their visual display size. Different lines can use differently sized fonts, so different lines will reach the right margin at different “columns”. In contrast the window sizes are counted in “number of standard-size char-cells” where the size of that standard char-cell depends on the default face (i.e. the font you specified in your default-frame-alist) used for that frame.

    In your screenshot, I see nothing that obviously explains the discrepency, tho: you seem to be using a normal monospaced font and all the text uses the same font, and you don’t seem to be using something like text-scale-increase, so I’m not sure exactly why you’re seeing what you’re seeing.

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