The preview feature of AUCTeX provides live rendering of TeX code at a user-specified preview scale. This package makes the preview scale vary in a natural way with the text scale and the monitor. In particular, it provides the command M-x preview-tailor-set-multiplier that allows you to adjust the preview scale for a given monitor.

Download this repository, install using M-x package-install-file (or package-vc-install, straight, elpaca, …), and add something like the following to your init file:

(use-package preview-tailor
  :demand
  :config
  (preview-tailor-init)
  :hook
  (kill-emacs . preview-tailor-save))

The function preview-tailor-init sets the customization variable preview-scale-function to a function internal to this package that provides the calculation, so make sure you don’t modify that variable elsewhere in your init file.

To adjust the multiplier for the current monitor, use M-x preview-tailor-set-multiplier.

The monitor-specific multipliers are stored in the variable preview-tailor-multipliers, an association list mapping lists of monitor attributes to numbers. The multiplier is calculated by finding the first entry in the list that matches the current monitor’s attributes. These multipliers are saved for future sessions in the dotfile .preview-tailor inside your user-emacs-directory. This separation keeps monitor settings, which may be specific to a given computer, independent of your init file, which you might synchronize across multiple computers.

The preview scale is determined by multiplying five factors:

1. The result of preview-scale-from-face.
2. The current text scale factor (adjusted via the text-scale-adjust commands, default bindings C-x C-+ and C-x C--).
3. A multiplier based on the current frame’s monitor attributes, set via M-x preview-tailor-set-multiplier, defaulting to 1.
4. An additional factor provided by the user customization preview-tailor-additional-factor-function (default is nil, meaning this factor is omitted).
5. The buffer-local variable preview-tailor-local-multiplier, which defaults to 1.

The last two factors add convenience for varying the preview scale in different settings. For example, I use preview in both LaTeX-mode and lean4-mode, with different preview scales. This is because I use buffer-face-mode in LaTeX-mode, but not in lean4-mode. To achieve this, I add a function to lean4-mode-hook that sets preview-tailor-local-multiplier to 0.7.