# How to Change the Default Font Size in the Middle of One Document?

Basically, I am trying to do something conceptually similar to the following though looks funny.

\documentclass[12pt]{article}
\begin{document}
This is a sentence.
\clearpage
\documentclass[8pt]{article}
This is a sentence.
\clearpage
\documentclass[12pt]{article}
This is a sentence.
\end{document}


I saw the EXTSIZES package, but am seeking something more primitive and closer to the default that requires no package. Must I repeat \begin{small} and \end{small} all the time? Many thanks.

You could try this:

\documentclass[12pt]{article}
\begin{document}
This is a sentence.

This is a sentence.

\fontsize{8}{9.6}\selectfont

This is a sentence.

This is a sentence.

\fontsize{12}{14.4}\selectfont

This is a sentence.

This is a sentence.
\end{document}


The second argument of \fontsize is the interline spacing. If I'm not wrong, it's generally 1.2 times the fontsize (see Why is the linespread factor as it is?).

Note: the footnote size is based on the documentclass size. So, if you have an entire page with tiny font size, the footnote can be bigger than the main text, which can be strange. It's probably a bad typographic idea to change the font size in the middle of a document by this way.

Edit after a comment:

Seems also compatible with math mode:

\documentclass[12pt]{article}
\begin{document}
This is a sentence.

$E=mc^2$

This is a sentence. $E=mc^2$.

\fontsize{8}{9.6}\selectfont

This is a sentence.

$E=mc^2$

This is a sentence. $E=mc^2$.

\fontsize{12}{14.4}\selectfont

This is a sentence.

$E=mc^2$

This is a sentence. $E=mc^2$.
\end{document}


• This can work very well for text, but it may not work for math. (I am not able to test.) – barbara beeton Jun 28 '19 at 13:41
• @barbarabeeton I have added an example with math mode. Seems correct, but perhaps you think about other things? – quark67 Jun 28 '19 at 13:51
• Your example does clearly work. That's good news. Thank you for the demonstration. (This may depend on how math font families are defined in different document classes.) – barbara beeton Jun 28 '19 at 13:55

You can't use the standard primitive tags like \documentclass, \begin{document} etc. more than one time in a document. It is better to use the font size controlling tags like \small, \footnotesize, etc.

\documentclass[12pt]{article}

\begin{document}

This is for test

If you want to decrease the font size for some particular text, then

{\footnotesize

...

\par}%%End of font size decrease

%start of normal text size%%

...

\end{document}