Different default font sizes

Question

I was wondering what the default different font sizes would be, expressed in points, when documentclass option set respectively to 10pt, 11pt and 12pt. Could anyone tell me the font sizes of chapter, section, subsection, ... in each case?

\documentclass[11pt]{report}
\begin{document}
  \chapter{Hello}
  \section{Hello again}
  \subsection{This is getting awkward}
  \subsubsection{Indeed}
  \paragraph{First paragraph}
  \subparagraph{Wannabe-paragraph}
\end{document}

Answer 1

size11.clo defines the font sizes in your case and report.cls specifies how they are used in the document. Starting in report.cls and considering the definition of chapters, we find the following:

\def\@makechapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \raggedright \normalfont
    \ifnum \c@secnumdepth >\m@ne
        \huge\bfseries \@chapapp\space \thechapter
        \par\nobreak
        \vskip 20\p@
    \fi
    \interlinepenalty\@M
    \Huge \bfseries #1\par\nobreak
    \vskip 40\p@
  }}

and:

\def\@makeschapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \raggedright
    \normalfont
    \interlinepenalty\@M
    \Huge \bfseries  #1\par\nobreak
    \vskip 40\p@
  }}

These definitions show that \huge is being used for the chapter name and number, while \Huge is used for the chapter title.

Turning to size11.clo, we find:

\newcommand\huge{\@setfontsize\huge\@xxpt{25}}
\newcommand\Huge{\@setfontsize\Huge\@xxvpt{30}}

Finally, in latex.ltx, we have:

\def\@xxpt{20.74}
\def\@xxvpt{24.88}

So we can see that the chapter name and number will be set in size 20.74 and the title will be set in size 24.88. Note that this file also shows us that 11pt uses size 10.95, whereas 10pt and 12pt use 10 and 12 respectively:

\def\@xpt{10}
\def\@xipt{10.95}
\def\@xiipt{12}