Why do Latex classes often have font size limitations?

Question

I am a new user of Tex and am planning to just forget Latex and write raw Tex documents. One of the major reasons for this is that nearly all the common Latex classes I have seen have seemingly crazy text size limitations. If I use a an ordinary word processor I can use any font I want between 8 points and 48 points or even larger. However, if I use the "article" class (a common suggestion for writing letters), I only have a choice of 10, 11 or 12 pt. Why is this?

Answer 1

Your question shows a misunderstanding, you can have fonts any size you like

\documentclass{article}
\usepackage{lmodern}
\begin{document}
{\fontsize{2pt}{3pt}\selectfont 1}
{\tiny 2}
3
{\Huge 4}
{\fontsize{4cm}{4cm}\selectfont 5}
\end{document}

the options that you mention are not font sizes or even lengths, they are option names that set a whole range of things, the default font size, the page size, vertical spaces used around display environments and lists etc.

The names are just vaguely reminiscent of lengths so you can remember what they do. the 10pt and 12pt options do, amongst other things, set the default font size to 10pt and 12pt respectively. The 11pt option doesn't set anything to 11pt, it sets the default font size to 10.95pt for historical reasons, but the option name is just a name.

For the default Computer Modern font family the font sizes are restricted to a range of sizes (but not just 10,11,12pt, the actual list of allowed sizes is 5pt 6pt 7pt 8pt 9pt 10pt 12pt 10.95pt 14.4pt 17.28pt 20.74pt 24.88pt) but that restriction is just for historical compatibility and if you add the fix-cm package you can have Computer Modern at any size, just as you can other font families such as the latin modern I used above.

Answer 2

The historical reason is that Donald E. Knuth shipped TeX with a font family that that came in different versions, proportioned for each of those sizes. Variable fonts and different optical sizes in the same font file would be decades in the future.

Also, the original LaTeX class option syntax doesn’t parse 10pt or 12pt as a number followed by a unit. There’s a small, finite set of size options, including 11pt. People might want to display a very large font for a title or the first letter of a chapter, but that could be handled with something like \fontsize. The standard LaTeX document classes were intended for math papers that would be printed out on a laser printer, and no one would choose a main font whose size was either illegible or would waste that much toner. (Which could be more expensive than gold.) If you want more flexibility than that, you load a class or package with a key=value option syntax.

Answer 3

I would say that 99% of my documents used a normal size of 10, 11 or 12pt. So the provided defaults simply cover the typically needed sizes.

It is not very difficult to create a 14pt or 20pt setup, not more difficult than setting up the font sizes for a plain TeX document. You can check the values in one of the .clo files and adjust them to your needs. Or if you want it easy, you can use a package like extsizes or classes like memoir or the KOMA bundle which have built-in options for more sizes.

Answer 4

You can overcome this limit by using the fontsize package (see the documentation for details). For example:

\usepackage[fontsize=13.3]{fontsize}

sets the normal size to 13.3pt and the line spacing to ~15.96pt.

The line spacing can also be declared explicitly (here is 14.5pt):

\usepackage{fontsize}
\changefontsize[14.5pt]{13.3pt}

You can see the values for all the available font sizing commands with the \printsamples command:

\documentclass{article}
\usepackage{cochineal}
\usepackage{fontsize}
%\sampletext{Hello world}
\begin{document}
\printsamples{13.6pt}{12.3pt}
\end{document}