[Tex/LaTex] the width of the standard paragraph indent in LaTeX’s article class

articleindentation

If no changes has been made to the settings of indentation of an article class LaTeX document, what is the width of the paragraph indent?

texdoc article in the terminal opens the Standard Document Classes for LaTeX version 2e manual. In section 6.2 Paragraphing I find the following line:

⟨10pt⟩ \setlength\parindent{15\p@}

The \p@ means 1pt … so I guess this would mean that the standard indent is 15 pt at a 10 pt text size? Is this correct?

Best Answer

The standard classes article and report use sizeXY.clo to set parameters for the XYpt option, that is 10pt (default), 11pt and 12pt.

In size10.clo we find

\if@twocolumn
  \setlength\parindent{1em}
\else
  \setlength\parindent{15\p@}
\fi

which means that the parindent is different in twocolumn mode than in one column typesetting. The command \p@ stands for a dimension register storing the value 1pt, so 15\p@ is equivalent to 15pt. In size11.clo there is

\if@twocolumn
  \setlength\parindent{1em}
\else
  \setlength\parindent{17\p@}
\fi

and in size12.clo there is

\if@twocolumn
  \setlength\parindent{1em}
\else
  \setlength\parindent{1.5em}
\fi

The same values are found in bk10.clo, bk11.clo and bk12.clo that are used by the book class.

Note that these values are set after a \normalsize declaration, but before \normalfont is issued, so the value of em is the one relative to the corresponding font in the Computer Modern family.

If you want to set a value of \parindent in em units relative to the document font, do

\AtBeginDocument{\setlength{\parindent}{1em}}

(or whatever value you prefer).

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