Subcaption package not doing what I want it to do

Question

I want to build a figure with 5 subfigures inside. The code I have goes as follows:

\begin{figure}[hbt]
\begin{subfigure}{0.4\textwidth}
\includegraphics[scale=0.25]{mi1}
\footnotesize{\caption{masa=$(0,0203 \pm 0,0001)\;kg$, $m=(2,43\pm 0,01)\; s^{-2}$, $b= (1,22 \pm 0,08)\; s^{-1}$, $R^2=0,990$. }}
\end{subfigure}
\begin{subfigure}{0.4\textwidth}
\includegraphics[scale=0.25]{mi2}
\footnotesize{\caption{masa=$(0,0401 \pm 0,0001)\;kg$, $m=(5,20\pm 0,03)\; s^{-2}$, $b= (3,6 \pm0,1)\; s^{-1}$, $R^2=0,990$.}}
\end{subfigure}
\begin{subfigure}{0.4\textwidth}
\includegraphics[scale=0.25]{mi3}
\footnotesize{\caption{masa=$(0,0503 \pm 0,0001)\;kg$, $m=(6,44\pm0,04)\; s^{-2}$, $b= (8,7 \pm0,1)\; s^{-1}$, $R^2=0,987$.}}
\end{subfigure}
\begin{subfigure}{0.4\textwidth}
\includegraphics[scale=0.25]{mi4}
\footnotesize{\caption{masa=$(0,0704 \pm 0,0001)\;kg$, $m=(9,32\pm0,05)\; s^{-2}$, $b= (11,9 \pm0,1)\; s^{-1}$, $R^2=0,987$.}}
\end{subfigure}
\begin{subfigure}{\textwidth}
\centering
\includegraphics[scale=0.25]{mi5}
\footnotesize{\caption{masa=$(0,0904 \pm 0,0001)\;kg$, \\ $m=(12,14\pm0,08)\; s^{-2}$, $b= (8,8 \pm \\ 0,2)\; s^{-1}$, $R^2=0,987$.}}
\end{subfigure}
\caption{Se representan las velocidades angulares que adquiere la placa cebra en función del tiempo cuando el sistema se encuentra acelerado angularmente por una masa variable que ejerce un torque a una distancia de $(0,01998 \pm 0,00001) \;m$  con respecto al centro de masa. En rojo se superpone la recta de regresión calculada por el método de cuadrados mínimos con su pendiente $m$.}
\end{figure}

The problem is with the last subfigure. I want to put it in the middle but if I use \linewidth, the caption of the subfigure begins at the beginning of the page and not where the subfigure actually is.

Could someone help out with this one?

Answer 1

Instead of setting the width of the last subfigure to \textwidth, set that as well to 0.4\textwidth, add \centering at the start of the figure, and perhaps an \hfill between the subfigures that are on the same line.

Some other comments:

• \footnotesize is not a macro that takes an argument, so to limit its effect you should use {\footnotsize ...\par}, not \footnotesize{..}. However, you shouldn't be using it for every subcaption the way you have, to change the font properties of subcaptions use \captionsetup, as in the code below.

• Units should be written in upright font, not in the default math font, so $m$ for example is wrong. A very nice package for typesetting numbers with units (or just numbers, or just units) is siunitx. I modified your captions to use this below.

\documentclass{article}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{subcaption}
\captionsetup[subfigure]{font=footnotesize,justification=raggedright}
\usepackage{siunitx}
\sisetup{
  output-decimal-marker={,},
  separate-uncertainty=true
}
\begin{document}

\begin{figure}[hbt]
\centering
\begin{subfigure}{0.45\textwidth}
\centering
\includegraphics[width=\linewidth]{example-image}
\caption{%
$\text{masa}=\SI{0,0203 \pm 0,0001}{\kg}$, $m=\SI{2,43\pm 0,01}{\per\square\s}$, $b= \SI{1,22 \pm 0,08}{\per\s}$, $R^2=\num{0,990}$. }
\end{subfigure}\hfill
\begin{subfigure}{0.45\textwidth}
\centering
\includegraphics[width=\linewidth]{example-image}
\caption{$\text{masa}=\SI{0,0401 \pm 0,0001}{\kg}$, $m=\SI{5,20\pm 0,03}{\per\square\s}$, $b= \SI{3,6 \pm0,1}{\per\s}$, $R^2=\num{0,990}$.}
\end{subfigure}

\begin{subfigure}{0.45\textwidth}
\centering
\includegraphics[width=\linewidth]{example-image}
\caption{$\text{masa}=\SI{0,0503 \pm 0,0001}{\kg}$, $m=\SI{6,44\pm0,04}{\per\second\squared}$, $b= \SI{8,7 \pm0,1}{\per\s}$, $R^2=\num{0,987}$.}
\end{subfigure}\hfill
\begin{subfigure}{0.45\textwidth}
\centering
\includegraphics[width=\linewidth]{example-image}
\caption{$\text{masa}=\SI{0,0704 \pm 0,0001}{\kg}$, $m=\SI{9,32\pm0,05}{\per\square\s}$, $b= \SI{11,9 \pm0,1}{\per\s}$, $R^2=\num{0,987}$.}
\end{subfigure}

\begin{subfigure}{0.45\textwidth}
\centering
\includegraphics[width=\linewidth]{example-image}
\caption{$\text{masa}=\SI{0,0904 \pm 0,0001}{\kg}$,  $m=\SI{12,14\pm0,08}{\per\square\s}$, $b= \SI{8,8 \pm 0,2}{\per\s}$, $R^2=\num{0,987}$.}
\end{subfigure}
\caption{Se representan las velocidades angulares que adquiere la placa cebra en función del tiempo cuando el sistema se encuentra acelerado angularmente por una masa variable que ejerce un torque a una distancia de \SI{0,01998 \pm 0,00001}{\m}  con respecto al centro de masa. En rojo se superpone la recta de regresión calculada por el método de cuadrados mínimos con su pendiente \si{m}.}
\end{figure}
\end{document}