How to handle overfull/underfull hbox

Question

i get an error message liks this

Overfull \hbox (2.37161pt too wide) in paragraph at lines 137--138

or

Underfull \hbox (badness 10000) in paragraph at lines 136--147

My code

\begin{figure}
\begin{subfigure}[c]{.7\textwidth}
\includegraphics[width=0.3\textwidth]{kurzpass.png}
\subcaption{Filterkurve eines typischen Kurzpassfilters\footnotemark}
\label{fig:kurzpass}
\end{subfigure}
%
\begin{subfigure}[c]{.7\textwidth}
\includegraphics[width=0.3\textwidth]{langpass.png}
\subcaption{Filterkurve eines typischen Langpassfilters\footnotemark}
\label{fig:langpass}
\end{subfigure}
\caption{\subref{fig:kurzpass} shows Figure1 and\subref{fig:langpass} shows Figure.}
\end{figure}

i do not get it

Answer 1

Those are warning messages, not error messages. Overfull \hboxes refer to having content that is too wide to fit within the text block width. In your case, you're placing twosubfigures next to one another - the % on the blank line between the two subfigures set them in the same line - each of which has a width of .7\textwidth. That results in something that is wider than \textwidth (1.4\textwidth to be exact) and results in the overfull \hbox warning.

For placing two subfigures next to one another, you're better off using .5\linewidth blocks, with the width of the internal images no more than \linewidth itself; \linewidth adjusts with the block it's placed in. \centering would also ensure that the content is horizontally centered.

Underfull \hbox warnings fall in a similar class in that there's not enough content to spread it across the text block sufficiently.