# How to choose font size given the paper size

How do you choose what font size to use given the paper size in use?

For example, I found somewhere that for a European standard the following is recommended:

\documentclass[a4paper,11pt]{article}
\usepackage[scale=0.7,vmarginratio={1:2},heightrounded]{geometry}


What is the typographic rule here? For example I want to print something (book, dissertation) on an A5 paper size. What should be the corresponding font size? How should I adjust the boundaries?

To be even more specific, in case it makes a difference, how this issue should be tackled when using the memoir document class?

## Edit:

Thanks to @cfr's answer, I'll state a more explicit case. I use the memoir class and it will be printed on A4 page. The class is loaded as:

\documentclass[11pt,a4paper,extrafontsizes,twoside]{memoir}
\fixpdflayout


Furthermore, I load the package \usepackage{fourier} to use the Utopia face. Finally, using the code snippet from 15 of the memoir class, I get the following output:

The length of this alphabet is 39.03668pt.

Should I do anything further?

• I think that also depends strongly on the purpose of the book. A dissertation is usually handed in on a4 paper, and when later published as a book just downscaled to a5 paper. – Martin - マーチン Aug 3 '13 at 11:51
• @Martin would you consider "downscaling" a typographically good practice? My understanding is that it is not enough. – Dror Aug 5 '13 at 7:53
• No, from a typographically point of view it is the poor-(wo)mans solution, but at least what I heard it is like common practice. On the other hand, if you are going to typeset the whole thesis on a5paper, you can do it right from the beginning. (I have only seen very few of this) However, I do not believe there are 'standards' for this case. – Martin - マーチン Aug 5 '13 at 11:43
• I have had a look at some books and came to the conclusion, that scale=0.8 and 10pt may be a good choice. The vmarginratio={1:2} is always a good option for twosided documents, as it gives you approximately 1:1:1 margins, when the book is opened. However, when dealing with a5paper it is quite crutial to set bindingoffset=5mm at least. This of course depends on the type of printer. Everything still also depend on the type of content, heads and foots... – Martin - マーチン Aug 5 '13 at 12:01
• Never. Ever. Scale. A. Font. There's a big difference between font size 7pt and for size 10pt scaled 70%. – yo' Nov 1 '13 at 15:55

The problem is not the font size nor the paper size, but the numbers of characters per line.

As noted in others answers, around the 65 ± 15 characters is considered a reasonable cut-off regardless the document type and even the font size.

When line of text are too long, your eyes will have a hard time focusing on the text. Its difficult find where the next line starts, specially in large paragraphs. Think in a landscape A0 poster with a single column of text ...

If the line
is too short
rhythm, since
the eyes will
have to travel
back too often.
This is so
annoying that
dancing eyes
can skip
some words.

You can roughly estimate the Average number of characters in one line. If you find that this number is out of a reasonable range, your options are basically:

1. Modify the margins. People are often obsessed with layouts that fit in mathematical ratios (golden ratio of 1.618:1, etc), geometrical rules, traditional styles, etc., but IMHO, the best way to judge a layout is your eyes, not any arbitrary type of complex algebra. Here you must consider mainly two factors:

a. Readability. Let these margins take the document in your hands without putting your fingers on the text? Do you see the text beside the inner margins of the book in a true 2D plane or in the border of a black hole? The part of the screen around the PDF is distracting you?

b. Appearance. The margin of a text, like a picture frame, is a ornament that highlight the content. The ornament depend of the text. A luxury book need big margins, but not a shopping list.

2. Modify the font size. Try to stay in the 10-12pt range as far as possible, but the important point is a comfortable viewing at about one arm's length (or more for a poster). In any case must be still easily readable, i.e, even if the line is less than 50 characters, do not use a 8pt characters for readers over 40 years. People with presbyopia will curse you for it. A very big font is harder to read too.

3. Use two or more columns. For any bigger pager size than a A4 paper is really a must. Magazines and newspapers always use mul­ti­ple-col­umn layouts for this reason, never single blocks of text with one inch margin or so. Even for articles in A4 with a 10pt, IMHO is more pleasant two columns with reasonable smaller margins than a single column with the default margins.

• As far as legibility is concerned, the size of the font in pts is not necessarily a good guide to the size of the font. That is, one font at 12pt may be quite small, while another at 10pt may be quite large. They vary a lot. (We are advised to use at least 14pt for all handouts for students in lifelong learning classes, although I generally use 12pt. I certainly think that 10pt TNR or 10pt CM is going to be somewhat difficult for some older students - not to mention some younger ones, as well.) – cfr Jan 9 '15 at 23:56

Depending on your usage context, the principal typographic consideration is likely to be the measure of your text i.e. how long in characters each line of text is.

A good rule of thumb is to adjust the font size to something that looks sensible* and then adjust your horizontal margins so that you get around 50-80 characters per line.

*10pt is pretty standard for a book, but certain things such as theses, journal manuscripts, or manuscripts on A4 paper or larger may demand a larger font.

• I know the 50-80 chars per line rule. How do I apply it in practice to a non-standard document? – Dror Jan 5 '15 at 5:08

Not necessarily improved...

I finally read the beginning of the memoir documentation, and things make a bit more sense. However, either there is a bug in the manual or I'm misreading it, or I have a quirky copy of Utopia because I think the sizes for the Utopia alphabets in the table should be shifted by one position. (Explanations below.)

To get sane results, you need to do some configuration before \documentclass. At least, this is how I read the instructions around page 3.

The code below is both an illustration of the method and an explanation of that method, along with a demonstration of its results.

## Note

As written, this question asks how to figure out which size font to use. One could try to do that by running memoir's method backwards. But I think it is better to start with a reasonable default (e.g. 11pt), figure out an appropriate layout based on that assumption and then adjust and re-calculate if needed.

For example, I conclude below that 11pt is probably rather small given the text width this ends up suggesting. So rerunning things with 12pt seems a good idea, and I run the calculations again with 12pt. (Obviously, I can't implement both in one document but you can change 11pt to 12pt and adjust the text width if you want to follow this recommendation.)

Part of the issue here is that I suspect the ideal recommendations are based on paper sizes rather different from A4. Most books are not printed on pages anything like that large unless they are reference books, often including illustrations and diagrams or set in multiple columns. So another option would be to use a different paper size or a two-column layout. If you plan to use lots of marginal notes, you probably don't need to worry as this will help to balance the page. But, if not, I think a single column of 11pt Utopia set up to get about 65-70 characters per line is going to look much too skinny on A4. Even 12pt is going to be pretty lean. (And beyond that, I think the font starts to look oddly large.) But, anyway, just some things to think about.

# Commented Code

This is not a standard MWE as the point here is really the comments and content rather than the code.

\newcommand*{\memfontfamily}{futs}% page 3 - you need to change this if you want a non-default option for fourier
\newcommand*{\memfontpack}{fourier}
\RequirePackage{fourier}\normalfont% from page 15
\documentclass[11pt,a4paper,extrafontsizes,twoside]{memoir}
% \usepackage{fourier}
\settrims{0pt}{0pt}% set trims - see page 22
\settypeblocksize{*}{110mm}{2}% the type block will have the ideal width (see below) and a height twice the width
\setbinding{0pt}% adjust if you need an allowance for binding
\setlrmargins{*}{*}{2}% the outer margin twice the width of the inner
\setulmargins{*}{*}{2}% lower margin twice the height of the upper
\setheadfoot{14pt}{28pt}% header height of 14pt and foot skip of 28pt - page 20
\setheaderspaces{*}{*}{.5}% drop the header by twice the distance from the header to the top of the text block
\setmarginnotes{7pt}{175pt}{10pt}% margin notes 7pt from text block, maximum width 175pt, minimum vertical sep 10pt
\setcolsepandrule{10pt}{0pt}% 10pt between columns in two-column layout, with no vertical rule drawn
\checkandfixthelayout
% \fixpdflayout% use this if not using pdfLaTeX

\begin{document}

\noindent Output from console:

\begin{verbatim}
******************************************************
Stock height and width: 845.04684pt by 597.50787pt
Top and edge trims: 0pt and 0pt
Page height and width: 845.04684pt by 597.50787pt
Text height and width: 636.60028pt by 312pt
Spine and edge margins: 94.83337pt and 189.6942pt
Upper and lower margins: 73.02856pt and 135.418pt
Footskip: 28pt
Columnsep and columnseprule: 10pt and 0pt
Marginparsep and marginparwidth: 7pt and 175pt
Sidecapsep and sidecapwidth: 7pt and 101pt
Sidebarhsep and sidebarwidth: 7pt and 101pt
Sidebarvsep and sidebartopsep: 13.6pt and 0pt
Sidebarheight: 594.32022pt
Sidefoothsep and sidefootwidth: 7pt and 101pt
Sidefootvsep and sidefootheight: 13.6pt and 594.32022pt
******************************************************
\end{verbatim}

\section*{Calculations}

Easier' method from page 15:

\setlxvchars \setxlvchars% page 15
\verb|\lxvchars| is \the\lxvchars{} and \verb|\xlvchars| is \the\xlvchars{}% \lxvchars is 308.77269ptand \xlvchars is 213.84044pt

But I'm not sure what to do with this information\dots

The original method from page 15:

% page 15
\newlength{\mylen}% a length
\newcommand{\alphabet}{abcdefghijklmnopqrstuvwxyz}% the lowercase alphabet
\begingroup% keep font change local
% font specification e.g., \Large\sffamily
\settowidth{\mylen}{\alphabet}
The length of this alphabet is \the\mylen. % print in document
\typeout{The length of the Large sans alphabet is \the\mylen}% put in log file
\endgroup% end the grouping

So the length of the alphabet appears to be $134$pt.
The package claims this is the length for $10$pt, using Utopia (table on page 16).
However, using $10$pt gives me a length of $125$pt.
So, let's go with $134$pt.

Turning to table 2.2 on page 14, a line width of $26$ pica would seem good (for an average 65 characters per line).

Using the conversion table on page xxxvi, we get an ideal text width of about $10.97$cm.

$26\textrm{pc} = 26 \times 12\textrm{pt} = 312\textrm{pt} = \frac{312}{72.27}" = 4.31" = 4.31 \times 2.54\textrm{cm} = 10.97\textrm{cm}$

Let's call it $11$cm i.e.\ $110$mm.
This is actually all we need to know to feed the package.
Memoir will calculate the rest if we just tell it our desired ratios.

However, we can also figure out what the results will be.
A4 is $210$mm wide, so we want about $100$mm for the margins in total.
Splitting this in the ratio 2:1 for a two-sided layout, we want an outer margin of about $66.6'$mm and an inner of about $33.3'$mm.

\section*{Which size of font?}

Memoir assumes that you will calculate the page layout given a selected font size.
But, of course, you could do this differently.
You could work backwards.
In practice, though, it is probably best to work forwards with an approximate choice, adjust if necessary and then re-calculate since you have to end up somehow with an integer point size for the font.

In this case, I think that the text block is disproportionately narrow.
So I'd rerun the calculations using a slightly larger point size.

If we try $12$pt, then we get an alphabet length of about $147$pt which suggests a text width of closer to $30$ pica.
$\frac{30 \times 12}{72.27} \times 2.54 = 12.65\textrm{cm}$
So we might try a text width of 125mm or so, which would give a still large but somewhat less huge outer margin of $5.6'$cm.

\end{document}
`

# Output

Just for the record:

• This is a very nice pointer. I find it still complicated to determine what should I set... – Dror Jan 1 '14 at 16:40
• Well memoir goes to some trouble to set up typographically decent defaults. So if you are using a fairly standard paper size and font, I'd think going with those defaults would be a good start unless you are typesetting a particularly unusual kind of document which memoir wasn't really designed for. Do the defaults seem unsatisfactory with your document? – cfr Jan 2 '14 at 1:01
• 1) The current result is, as far as my untrained eyes can say, OK. 2) I also fund the ~39pt(!) suspicious. 3) I can (probably) somehow handle the computations, but I get lost in the technical part. – Dror Jan 2 '14 at 5:58
• @Dror I had another go at this - see new answer above. The 39pt is wrong. When I implement the code from the introduction, I get a saner 134pt. (Which is still not what the manual gives for Utopia but those values seem to be shifted by a position or so? Or have I missed something?) Anyway, I think it makes more sense now! – cfr Jan 5 '15 at 1:50

I suggest that the answer to your question significantly varies with what other features of the text coexist with natural language on the page, and with the content of the text. In other words, what is the background to the text, in the sense of these other objects, and what information is conveyed by the text.

Font size is not merely determined by size of the paper.

For example, if you have mathematics, I have found 55 to 57 characters, including space and punctuation, per line. Books with the usual 65 to 67 characters per line are much LESS pleasing to read, especially when equations are periodically littered throughout the text. The font size is appropriate to realize this.

More abstract technical literature (A) often uses 55 to 57, if mathematical in content. Specialized mathematical literature (B) uses 65 to 67. Journals often go 77 to 79.

Fewer characters requires larger characters; try to font size and count the characters, INCLUDING SPACES AND PUNCTUATION, in typical sentences.

Insert a few short equations and you'll see how nicer the larger (but not too large). Vary the count slightly to make the text coherent with the equations, so that nothing JUMPS OUT in contrast and irritates. That's the key to stress-free reading.

I seriously recommend going for 55 to 57, in the memoir class, since you have control over this (as opposed to where you submit to a journal).

If you have no images or equations, you can go up to 65 to 67 (B), as is now usually the case, but I also find non-mathematical text more pleasant reading with 57 to 59, which is closer to (A).

This is partly a matter of taste, so pick up a non mathematical book whose typography you enjoy and count the measure. Do the same for a mathematical book.

A paperback novel, for comparison, has a smaller page and smaller font, but it usually has 63 to 65 characters per line. Again, for comparison, a larger book bound in leather, a theoretical text, from the 1870's has 45 to 47, on a page, and slightly larger margins than conventional; another book, with identical page size, from the 1970's, has 65 to 67, again. This however is the limit, I think, to ease of readability. Ever notice why you slow down while reading journal articles? Neither contains equations. Yet each is substantially larger in size than the paperback novel. A large hardcover quasi-popular scientific monograph, from 2013, contains 53 to 55. It's almost three times the page area of the paperback.

Font size is easy to set in the preamble, and you're no changing margins, I see, so let's analyse the last paragraph.

The basic reason why some typography is hard to read and other typography is not has been considered. Hebb (1949) pointed out, and it is well known today, that the eye does not read the whole page at once, nor does it really scan line by line, but it moves such as to aid what the brain is doing at the moment, which is trying to separate foreground from background, and oscillating back and forth between foreground and background when these are identified, to keep the image clear. The result is integrated and parsed.

The font must not be neither to small, nor too close together, to require careful attention to unconsciously separate the letters. It must also not contrast to much with other components of the text, like mathematical formulae, if any, because if it does, when the formulae are perceived as foreground, the other text becomes background, and vice versa, which is unconsciously distracting and interrupts rapid reading, because the text is no longer parsed together with the equations with which it is, content wise, one thought, one sentence.

In the examples, the content is the deciding factor. If the designer anticipates people to focus on word by word phrasing, like a work of fiction, or a book of philosophy, or an essay chapter, a larger measure (B), would not substantially annoy, regardless of page size, but it does not scale with the page size, only becomes slightly larger.

If the designer anticipates readers to parse the text and think about the concepts in the texts at the same time, so that they are less attentive to the exact wording of the text, a smaller measure is appropriate, because they are not paying so much attention to the words on the page, and the typography must be easier to separate as a whole from its background, since less attention goes to analysing the page, and more to what the text on the page describes.