settosize – Scale text to given width
The package defines a command
\set <text> \in <font> \to <size>
that chooses the “best” magstep that will fit the given text into the width, and typesets the text accordingly.
Maybe you are interested in the following packages as well.
- fontch: Changing fonts, sizes and encodings in Plain TeX
- plnfss: Font selection for Plain TeX
- ofs: Macros for managing large font collections
- gkpmac: The macros used in "Concrete Mathematics"