Text alignment with different size

Question

With this code:

\documentclass{minimal}
\usepackage[a4paper,showframe]{geometry}
\begin{document}
\noindent
\sffamily
Foo\\
\fontsize{24}{24}\selectfont
Bar
\end{document}

I get this output:

How can I left align the two lines?

Answer 1

TeX doesn't know the width of a glyph of a font. It only knows the width of the surrounding box. If you enclose the character in a \fbox you can see, how much TeX knows about the two glyphs you want to align:

\documentclass{minimal}
\usepackage[a4paper,showframe]{geometry}
\fboxsep=-\fboxrule
\begin{document}
\noindent
\sffamily
\fbox{F}oo\\
\fontsize{24}{24}\selectfont
\fbox{B}ar
\end{document}

As you can see, the characters are aligned as far as TeX is concerned, therefore you'll have to align them manually, e.g. with:

\documentclass{minimal}
\usepackage[a4paper,showframe]{geometry}
\begin{document}
\noindent
\sffamily
Foo\\
\fontsize{24}{24}\selectfont
\hspace*{-0.12ex}Bar
\end{document}