I tried \documentclass[11,5pt]{book}, but received LaTeX Warning: Unused global option(s): [11,5pt].
[Tex/LaTex] Can you set a font at 11,5
fonts
Related Solutions
LaTeX needs to see a \DeclareFontFamily declaration before a \DeclareFontShape command can be issued.
A simple way out is to add
\sbox0{\ttfamily X}
after \usepackage[<options>]{beramono}, which will cause the corresponding .fd file to be read in, which contains the appropriate \DeclareFontFamily command.
The latest version [2013/09/23] of sourcesanspro.sty loads the mweights.sty to exactly cope with such issues. mweights.sty provides means for specifying e.g. different bold weights for roman, typewriter and sans serif fonts. Compiling your code with this newer package gives:
Note that the log contains the information
LaTeX Font Info: Font shape `T1/gentium/bx/n' in size <12> not available (Font) Font shape `T1/gentium/b/n' tried instead on input line 22.
Showing that an attempt has been made to load it at weight bx, but this was not found and b was used instead.
Best Answer
You can use a font of that size
\fontsize{11.5}{12}\selectfontbut the options to book are not lengths they are just names of options and there are just three that look a bit like lengths: 10pt, 11pt, 12pt, and they do a lot more than set a font size they set the page size, the size of all the named sizes etc.