# Change font size only in a part of a document

I have created my thesis using mathptmx size 12pt. I would use in only a part Latin Modern but not 12pt instead 11pt. How can I achieve that? I tought to \small but I don't know if correspond to the correct size

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for the basic latex document classes, in fact \small is 11pt when option 12pt is used. this is set in the file size12.clo (or a comparable one for the book class) with the code \newcommand\small{\@setfontsize\small\@xipt{13.6}..., where \@xipt designates 11pt using the roman numeral to construct a valid alphabetic command name. –  barbara beeton Jan 18 '13 at 16:20
@barbarabeeton, is 13.6 the value for \baselineskip here? –  Sigur Jan 18 '13 at 16:33
13.6 is the value set for 11pt text in both size12.clo and bk12.clo. (you didn't say what document class you're using.) the ams document classes use 13 for \small in a 12pt document. so different publishers have different opinions on the subject. check your document .cls file (if it has the values built in) or your .log file to see what .clo files are read in and check there. –  barbara beeton Jan 18 '13 at 16:42

When the font size in document is set as 12pt, the definitions are used from the file size12.clo (you can see it in the log file). size12.clo defines \small as

\newcommand\small{%
\@setfontsize\small\@xipt{13.6}%
\abovedisplayskip 11\p@ \@plus3\p@ \@minus6\p@
\abovedisplayshortskip \z@ \@plus3\p@
\belowdisplayshortskip 6.5\p@ \@plus3.5\p@ \@minus3\p@
\def\@listi{\leftmargin\leftmargini
\topsep 9\p@ \@plus3\p@ \@minus5\p@
\parsep 4.5\p@ \@plus2\p@ \@minus\p@
\itemsep \parsep}%
\belowdisplayskip \abovedisplayskip
}


Hence \small is using 11pt size. Hence you can use \small.

The other method is to use \fontsize{<font size>}{interline skip>}\selectfont where the interline skip is usually 120% of font size.

\documentclass[12pt]{article}
\usepackage{mathptmx}
\usepackage{lipsum}

\begin{document}
\lipsum[1]
\noindent
\begin{tabular}{*{2}{p{.47\textwidth}}}\hline
{   %% Open a group to make the effect of \small local
\small
\lipsum[1]
}   %% Close the group
&
{
\fontsize{11}{13.6}\selectfont
\lipsum[1]
}\\\hline
\end{tabular}
\end{document}


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foo{\fontsize{11pt}{13.2pt}\selectfont foo}foo


The first number is for the font size and the second one is for \baselineskip, usually 1.2 times the font size.

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a changed \baselineskip won't take effect unless it's the value in effect when a paragraph break occurs. so although it's always a good idea to use an appropriate value, in the case shown here, it could even be 0pt or 30pt with no effect. –  barbara beeton Jan 18 '13 at 16:14