What is the default font size of a LaTeX document?

What is the default font size of a LaTeX document?

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It depends on the font-related options and the argument of the \documentclass[<options>]{<class-name>} command. Assuming you're use a basic document class (such as article) and don't provide font-related options, the default font size will be 10pt. –  Mico Jan 25 '14 at 15:24
No less important, perhaps, is the value for \baselineskip, which is equal to (about) 1.2 times the fontsize unless fiddled with. Thus a simple \the\baselineskip will print the value for \baselineskip right in your document. (Simple math to work backwards to the fontsize value.) Also the standard classes will usually load, right after the .cls file, a .clo file (something like size10.clo), which is where many of these 'size' values are initially set. –  jon Jan 25 '14 at 15:42
–  texenthusiast Jan 25 '14 at 16:56

10pt is the default font size unless you opt for other available sizes.

Depends on the document class you are using, but mostly it is 10pt.

• article: Default is 10 pt, other available options are 11 pt and 12 pt.
• book: Default is 10 pt, other available options are 11 pt and 12 pt.
• report: Default is 10 pt, other available options are 11 pt and 12 pt.
• letter: Default is 10 pt, other available options are 11 pt and 12 pt.
• proc: Default is 10 pt, other available options are 11 pt and 12 pt.
• ext versions of the above (extarticle,extreport, extbook, extletter, and extproc) (the extsizes): Again, Default is 10 pt, other available options are 8pt, 9pt, 11pt, 12pt, 14pt, 17pt, and 20pt.
• The ams class (amsart, amsbook and amsproc), coming from the ams-LaTeX collection prepared by the American Mathematical Society: Default is 10 pt, other available options are 11 pt and 12 pt.
• memoir: Default is 10 pt, other available options are 9pt, 11pt, 12pt, 14pt, 17pt, 20pt, 25pt, 30pt, 36pt, 48pt,60pt. Option extrafontsizes is available to indicate that you will be using scalable fonts that can exceed 25pt.
• beamer: Default is 11 pt, other available options are 8pt, 9pt, 10pt, 11pt, 12pt, 14pt, 17pt, 20pt.
• koma-script (scrartcl, scrbook, and scrreprt): Default is 11 pt. KOMA-Script does not use fixed fonts and attributes to emphasize different elements of the text. Instead there are variables that contain the commands used for changing fonts and other text attributes.

This one (What are the available “documentclass” types and their uses?) will answer many supplementary questions you might have.

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the ams document classes equivalent to article, book and proc are in the "latex required" collection distributed as part of tex live. if you want to add a "group" item to this list, they default to 10 pt, with options 11pt and 12pt. (ams classes differ from the base classes with respect to the top matter (input format and output presentation), and by the inclusion of amsthm, amsmath and amsfonts, but otherwise conform to the structure of the base classes to allow easy substitution.) –  barbara beeton Jan 25 '14 at 16:46
For a bit of background on KOMA-Scripts fontsize selection: tex.stackexchange.com/q/108569 –  clemens Jan 25 '14 at 16:51
@barbarabeeton When you make a list, you always run the risk of omissions. Thanks a lot. Added. –  Masroor Jan 25 '14 at 16:57
Default is 10 pt for article report book letter except slides From LaTeX Reference manual: 4.1 Document class options –  texenthusiast Jan 25 '14 at 17:04
@MMA thank you for your nice explanation. From where did you get the information about the standard classes like article, book, report, letter? –  John Threepwood Jan 25 '14 at 19:04

The KOMA-Script classes scrartcl, scrbook, and scrreprt -- unlike the standard classes and memoir -- feature a default font size of 11pt, which allows for typographically sound margins when using the paper sizes A4 or letter. With KOMA-Script, it is also possible to select any desired font size and specify it in any TeX unit of measure. See section 3.5 of the KOMA-Script manual for details.

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Based on a Mike Renfro's answer to How can I test for the current font?. \f@size is the internal macro that holds the current font size.

Without specifying additional font size options to document class one can test the default font size. For example slides has default font size of ~20 pt

\documentclass{slides}
\makeatletter
\newcommand{\showfontsize}{\f@size{} pt}
\makeatother
\begin{document}
The current font size is \showfontsize
\end{document}


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No idea why it shows 19.907 pt not 20 pt exactly unlike 10 pt ? –  texenthusiast Jan 25 '14 at 17:58
It's been many, many years since I last used the slides document class. Is there any reason (other than inertia...) for still using slides if beamer is an option? –  Mico Jan 25 '14 at 18:00
@Mico it's only my curiosity to find the default font size for a not widely used document class :). I do use beamer –  texenthusiast Jan 25 '14 at 18:03