# 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.

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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