# [NTG-context] what defines the font size?

Pablo Rodriguez oinos at gmx.es
Tue Oct 16 19:48:41 CEST 2018

```On 10/15/18 10:02 PM, Ulrike Fischer wrote:
> Am Mon, 15 Oct 2018 21:21:32 +0200 schrieb Pablo Rodriguez:
>> [...]
>> If two fonts have the same size, I think there may be a dimension which
>> has the same length in both. Which one is this?
>
> None. The font decides about its size.

Many thanks for your clear statement, Ulrike.

Thomas Pinney explains why this might happen:
http://www.thomasphinney.com/2011/03/point-size/.

I cannot claim that I understand his explanation, but it seems that
there is something about the em quad, which might be something like:

\setupframed
[offset=none,
framecolor=red,
rulethickness=0.01pt,
width=12pt,
height=12pt]

\starttext
\startTEXpage[offset=1em]
\framed{M}
\framed{\tfxx M}
\framed{\tfd M}
\stopTEXpage
\stoptext

The square gives the points of the font (its size), but the glyphs might
be drawn in many different ways (I guess).

The issue with units per em is something I didn’t understand.

I tried to experiment (modifying TeX Gyre Pagella from 1000 to 9999
UPM), but for some reason, I wasn’t able to load the font.

Just in case anyone wonders, my code was standard:

\definefontfamily
[mainface]
[rm]
[TeX Gyre Pagella]
[bf=file:texgyrepagella-modified.otf]
\setupbodyfont[mainface]

And the file was on the same directory as my ConTeXt source file.