How to set the font size in Emacs?

(set-face-attribute 'default nil :height 100)

The value is in 1/10pt, so 100 will give you 10pt, etc.

From Emacswiki, GNU Emacs 23 has a built-in key combination:

C-xC-+ and C-xC-- to increase or decrease the buffer text size

Press Shift and the first mouse button. You can change the font size in the following way: This website has more detail.

M-x customize-face RET default will allow you to set the face default face, on which all other faces base on. There you can set the font-size.

Here is what is in my .emacs. actually, color-theme will set the basics, then my custom face setting will override some stuff. the custom-set-faces is written by emacs's customize-face mechanism:

;; my colour theme is whateveryouwant :)
(require 'color-theme)
(color-theme-initialize)
(color-theme-whateveryouwant)

(custom-set-faces
  ;; custom-set-faces was added by Custom.
  ;; If you edit it by hand, you could mess it up, so be careful.
  ;; Your init file should contain only one such instance.
  ;; If there is more than one, they won't work right.
 '(default ((t (:stipple nil :background "white" :foreground "black" :inverse-video nil :box nil :strike-through nil :overline nil :underline nil :slant normal :weight normal :height 98 :width normal :foundry "unknown" :family "DejaVu Sans Mono"))))
 '(font-lock-comment-face ((t (:foreground "darkorange4"))))
 '(font-lock-function-name-face ((t (:foreground "navy"))))
 '(font-lock-keyword-face ((t (:foreground "red4"))))
 '(font-lock-type-face ((t (:foreground "black"))))
 '(linum ((t (:inherit shadow :background "gray95"))))
 '(mode-line ((t (nil nil nil nil :background "grey90" (:line-width -1 :color nil :style released-button) "black" :box nil :width condensed :foundry "unknown" :family "DejaVu Sans Mono")))))

This is another simple solution. Works in 24 as well

(set-default-font "Monaco 14")

Short cuts:

`C-+` increases font size
`C--` Decreases font size

I've got the following in my .emacs:

(defun fontify-frame (frame)
  (set-frame-parameter frame 'font "Monospace-11"))

;; Fontify current frame
(fontify-frame nil)
;; Fontify any future frames
(push 'fontify-frame after-make-frame-functions) 

You can subsitute any font of your choosing for "Monospace-11". The set of available options is highly system-dependent. Using M-x set-default-font and looking at the tab-completions will give you some ideas. On my system, with Emacs 23 and anti-aliasing enabled, can choose system fonts by name, e.g., Monospace, Sans Serif, etc.

Open emacs in X11, goto menu Options, select "set default font ...", change the font size. Select "save options" in the same menu. Done.

zoom.cfg and global-zoom.cfg provide font size change bindings (from EmacsWiki)

C-- or C-mousewheel-up: increases font size.

C-+ or C-mousewheel-down: decreases font size.

C-0 reverts font size to default.

Firefox and other programs allow you to increase and decrease the font size with C-+ and C--. I set up my .emacs so that I have that same ability by adding these lines of code:

(global-set-key [C-kp-add] 'text-scale-increase)

(global-set-key [C-kp-subtract] 'text-scale-decrease)

Here's an option for resizing the font heights interactively, one point at a time:

;; font sizes
(global-set-key (kbd "s-=")
                (lambda ()
                  (interactive)
                  (let ((old-face-attribute (face-attribute 'default :height)))
                    (set-face-attribute 'default nil :height (+ old-face-attribute 10)))))

(global-set-key (kbd "s--")
                (lambda ()
                  (interactive)
                  (let ((old-face-attribute (face-attribute 'default :height)))
                    (set-face-attribute 'default nil :height (- old-face-attribute 10)))))

This is preferable when you want to resize text in all buffers. I don't like solutions using text-scale-increase and text-scale-decrease as line numbers in the gutter can get cut off afterwards.

Aquamacs:

(set-face-attribute 'default nil :font "Monaco-16" )

From the Emacs Wiki Globally Change the Default Font, it says you can use either of these:

(set-face-attribute 'default nil :font FONT )

(set-frame-font FONT nil t)

Where FONT is something like "Monaco-16", e.g.:

(set-face-attribute 'default nil :font "Monaco-16" )

There was an extra closing parenthesis in the first suggestion on the wiki, which caused an error on startup. I finally noticed the extra closing parenthesis, and I subsequently corrected the suggestion on the wiki. Then both of the suggestions worked for me.

It all depends what you mean by change the font size. This EmacsWiki section provides the best and most complete information. It distinguishes the various cases (text scaling, frame font, buffer/frame, etc.): Changing Font Size.

In AquaMacs CMD + and CMD - adjust the font size for the current buffer.

In NTEmacs 23.1, the Options menu has a "Set default font..." option.

I you're happy with console emacs (emacs -nw), modern vterm implementations (like gnome-terminal) tend to have better font support. Plus if you get used to that, you can then use tmux, and so working with your full environment on remote servers becomes possible, even without X.

I use hydra package to control font increase/decrease contiguously by pressing f2 + + + +/f2 - - - -, which means that press f2 once, and then using +/- to control only, and restore default font size by f2 0. Because i have keypad, so I also bind keypad to the font setting.

(defhydra hydra-zoom (global-map "<f2>")
  "zoom"
  ("<kp-add>" text-scale-increase "in")
  ("+" text-scale-increase "in")
  ("-" text-scale-decrease "out")
  ("<kp-subtract>" text-scale-decrease "out")
  ("0" (text-scale-set 0) "reset")
  ("<kp-0>" (text-scale-set 0) "reset"))

And modern editor mouse control functionality supported by below key bindings, press control + mouse wheel to increase/decrease font.

(global-set-key (kbd "<C-wheel-up>") 'text-scale-increase)
(global-set-key (kbd "<C-wheel-down>") 'text-scale-decrease)

Here's a snippet that lets you directly specify the global font size using an interactive function:

(defun set-font-size ()
    "Set the font size."
  (interactive)
  (set-face-attribute
   'default nil :height
   (string-to-number
    (read-string "Font size: " (number-to-string (face-attribute 'default :height nil))))))