How to set the font size in Emacs?

Question

I also want to save the font size in my .emacs file.

Answer 1

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.