According to the
documentation
or (info "(org) Previewing LaTeX fragments")
You can customize the variable `org-format-latex-options' to
influence some aspects of the preview. In particular, the `:scale'
(and for HTML export, `:html-scale') property can be used to
adjust the size of the preview images.
A quick
C-hvorg-format-latex-options
RET
gives us:
org-format-latex-options is a variable defined in `org.el'.
Its value is (:foreground default :background default :scale 1.0 :html-foreground "Black" :html-background "Transparent" :html-scale 1.0 :matchers
("begin" "$1" "$" "$$" "\\(" "\\["))
Documentation:
Options for creating images from LaTeX fragments.
[snip]
:scale a scaling factor for the size of the images, to get more pixels
[snip]
For example, to set the scale to 2.0
:
(setq org-format-latex-options (plist-put org-format-latex-options :scale 2.0))