What point (pt) font size are \Large etc.?

The font changing commands are often determined by the document class itself. For the standard classes (with size options in the first row), the values are as follows:

Command             10pt    11pt    12pt
\tiny               5       6       6
\scriptsize         7       8       8
\footnotesize       8       9       10
\small              9       10      10.95
\normalsize         10      10.95   12
\large              12      12      14.4
\Large              14.4    14.4    17.28
\LARGE              17.28   17.28   20.74
\huge               20.74   20.74   24.88
\Huge               24.88   24.88   24.88

Other classes (especially the major document classes such as KOMA and Memoir) may have different values. The following document will print out the font sizes for all the standard size changing commands. You can use it to check font sizes for other classes.

\documentclass[11pt]{article}

\makeatletter
\newcommand\thefontsize[1]{{#1 The current font size is: \f@size pt\par}}
\makeatother

\begin{document}
\sffamily
\thefontsize\tiny
\thefontsize\scriptsize
\thefontsize\footnotesize
\thefontsize\small
\thefontsize\normalsize
\thefontsize\large
\thefontsize\Large
\thefontsize\LARGE
\thefontsize\huge
\thefontsize\Huge
\end{document}

See also the source code of standard document classes.

In classes.dtx: 6.1 Fonts.

Or size10.clo, size11.clo and size12.clo in $TEXMF/tex/latex/base/.

For example, in size10.clo:

\newcommand\small{%
   \@setfontsize\small\@ixpt{11}%
   \abovedisplayskip 8.5\p@ \@plus3\p@ \@minus4\p@
   \abovedisplayshortskip \z@ \@plus2\p@
   \belowdisplayshortskip 4\p@ \@plus2\p@ \@minus2\p@
   \def\@listi{\leftmargin\leftmargini
               \topsep 4\p@ \@plus2\p@ \@minus2\p@
               \parsep 2\p@ \@plus\p@ \@minus\p@
               \itemsep \parsep}%
   \belowdisplayskip \abovedisplayskip
}

A short overview of font sizes in the »LaTeX2e Reference Manual« might be helpful.