# How to determine the true size of a font?

A colleague of mine is submitting a research proposal to one of the UK research councils, whose guidelines stipulate a minimum font-size of 10pt. My colleague, who is of course using LaTeX, uses the amsart document class with the 10pt option (which, in fact, I think it's the default). Looking at the .log file one sees that the 10pt version of the fonts are indeed being loaded.

However word has come back that the proposal falls foul of the research council's guidelines because the font-size in the PDF file that my colleague submitted is actually 9.6pt! Alas, no information has been given as to how this font-size was determined.

### Questions

1. When is 10pt not really 10pt?

2. And how can one determine the true font size of a LaTeX-generated PDF document?

This just in: it seems that the culprit was the default scaling of helvetica, which according to the PSNFSS2e documentation (PDF file) is smaller than 1.

This still leaves the second question.

• Not the problem, but worth knowing anyway: there isn't a single width of a point, but several: see oberonplace.com/dtp/fonts/point.htm - in particular the difference between Tex and Postscript points (1/72.27 and 1/72 inch, respectively) is a real nuisance. – Charles Stewart Aug 9 '10 at 15:33
• Thanks - I knew about the many different points, although I confess I didn't think to check whether this could be the source of the problem. As you point out, the difference in the point size does not account for such a discrepancy in this case. – José Figueroa-O'Farrill Aug 9 '10 at 15:44
• Unless you are using a phototypesetter, be kind to your reviewers and use 11pt or greater thus obviating the problem. The definitive answer would come from the rejecting research council. Also, even if you agree on what size a point is, there is significant variation in the definition of what size a fontface is. – msw Aug 10 '10 at 2:29
• msw: thanks -- can you point to some literature on (attempts at) a precise definition of the size of a fontface? I'm curious. Thanks in advance. – José Figueroa-O'Farrill Aug 10 '10 at 17:27
• precise definition of the size of a fontface - The em-size the font designer states, the height of the tallest glyph in a font, and the vertical space Tex allocates to the text typeset in a font can all be different. The first is the usual measure, but you can't infer it from measuring the glyphs. This might be a good question to ask here. – Charles Stewart Aug 11 '10 at 6:30

PDFedit will be able tell you what the size of particular bit of text in a PDF document is.

• A hint on how would be great. – bluenote10 Apr 8 '14 at 12:47

Adobe Acrobat professional: Tools -> Advanced Editing -> Touchup text tool. Select text, right click -> Properties. Text tab, Font Size box.

• Thanks. Alas, I do not have access to this software. I did download the Acrobat Reader (for which I have no other use in principle) since I had vague memories that it did have a way to show the fonts being used, but it only gave the names of the fonts, their encoding,... but no information on the size beyond the one gleaned from the name of the font. – José Figueroa-O'Farrill Aug 9 '10 at 15:53

There are several definitions of the word “point,” and LaTeX itself has two different units, the pt and the bp (for “big point”).

Since you say that’s a minimum size, the easiest solution is probably to load \documentclass[11pt].

With fontspec and a modern TeX engine, you have the option of setting \defaultfontfeatures{ Scale = MatchUppercase } and then loading your main font with \setmainfont[Scale = 1.042]. (Or 4.2% higher than whatever it’s at now.) This should scale your main font to the size the publisher requested, and scale all the other fonts in the document to the same height.

If you’re using 8-bit fonts, many legacy font packages support a scale= option.

• Note that with the KOMA-Script classes, you can use bp as a measurement directly without having to change the scaling, e.g. \documentclass[fontsize=12bp]{scrartcl}. – Andrew Dunning Jan 22 '19 at 21:22
• @AndrewDunning Yes, although I don’t think that this could be a simple 10bp fix unless the point size given in the OP is a typo. – Davislor Jan 22 '19 at 21:35
• Yes, I'm sure that's not the problem in the original question; no doubt it was accidentally setting the Scale option (as I discuss more in my answer). – Andrew Dunning Jan 22 '19 at 21:37
• @AndrewDunning That’s possible. The OP doesn’t give a MCVE, which makes it harder for us to figure out what’s going on. – Davislor Jan 22 '19 at 21:41

This question is related to many other questions dealing with "font size". I wrote this simple tex file for myself. I have taken out my (pure XeTeX) formatting commands so as to make it readable and changeable. See the attached PDF file where the font was Libertine Roman at a nominal point size of 12.5pt

### Introductory material

When we speak of the point size of a classical (i.e. engraved in metal) this is a nominal value. Each character will have a different combination of height (total distance above the base line), depth (total distance below the base line) and width. Similarly in TeX if we define a font to have a size of 14.0 pt then 14.0 points is the nominal size. In TeX we can precisely determine the above values by looking at the bounding box of a letter. We do this by placing the letter, or letters, in a hbox and the using the command \the as applied to the \ht, \dp and \wd of the box.

Suppose that we are interested in the letter "g", which dips below the baseline. We first write:

\setbox0 \hbox{g}


and then determine the values as follows:

height = \the\ht0

depth =  \the\dp0

width =  \the\wd0


Here is the entire program:

\setbox0 \hbox{g}

\centerline {
height = \the\ht0
depth =  \the\dp0
width =  \the\wd0
}


We can also obtain the maximum range for a given nominal point size by placing the entire alphabet inside a hbox:

\setbox1 \hbox{abcdefghijklmnopqrstuvwxyz}
\centerline {
height = \the\ht1,\qq
depth =  \the\dp1,\qq
width =  \the\wd1
}


link 2 original TEX file (plain XeTeX, the macro commands are available link to macro files if desired

Many documents include Scale=MatchLowercase or Scale=MatchUppercase as default font features with fontspec, which makes sense, except that this causes the package to scale the main font against the prior default (normally Latin Modern). To check what LaTeX considers to be the font size, you can use something like this:

\documentclass[12pt]{article}
\usepackage{fontspec}
\defaultfontfeatures{Scale=MatchLowercase}
% font will be rendered at 11.02771pt with the following line removed
\defaultfontfeatures[\rmfamily]{Ligatures=TeX,Scale=1}
\setmainfont{TeX Gyre Pagella}

\begin{document}

The quick fox --- \the\fontdimen6\font\relax

\end{document}