To increase the height of the default face in the current buffer,
type C-x C-+ or C-x C-=. To decrease it, type C-x
C--. To restore the default (global) face height, type C-x
C-0. These keys are all bound to the same command,
text-scale-adjust, which looks at the last key typed to
determine which action to take.
Similarly, scrolling the mouse wheel with the Ctrl modifier pressed, when the mouse pointer is above buffer text, will increase or decrease the height of the default face, depending on the direction of the scrolling.
The final key of these commands may be repeated without the leading
C-x. For instance, C-x C-= C-= C-= increases the face
height by three steps. Each step scales the text height by a factor
of 1.2; to change this factor, customize the variable
text-scale-mode-step. A numeric argument of 0
text-scale-adjust command restores the default height,
the same as typing C-x C-0.
text-scale-decrease increase or decrease the height of the
default face, just like C-x C-+ and C-x C-- respectively.
You may find it convenient to bind to these commands, rather than
text-scale-set scales the height of the default
face in the current buffer to an absolute level specified by its
The above commands automatically enable the minor mode
text-scale-mode if the current font scaling is other than 1,
and disable it otherwise.