Gnuplottex font size to whole graph

Question

I would like to change font size of general graph generated by gnuplottex, I've got this code

\documentclass[8pt,a4paper,dvipsnames]{article}
\usepackage[utf8]{inputenc}
\usepackage[left=2cm,right=2cm,top=1.5cm,bottom=1.5cm]{geometry}

\usepackage{gnuplottex}
\begin{document}

\begin{figure}[htp]
    \centering
    \begin{gnuplot}[scale=1.3, terminal=epslatex, terminaloptions={color dashed font ",3"}]
        set samples 50000
        set grid
        set key box
        set xrange [-3:1]
        set yrange [-5:30]

        p x**2
    \end{gnuplot}
    \caption{parabolic curve} \label{fig:Parab}
\end{figure}


\end{document}

But font is not scaled, instead of I get the following

Answer 1

I had another solution here first, but I worked out a more proper one.

The font size you pass to Gnuplot only controls how much space Gnuplot uses for each label. The actual characters are typeset by Latex. So, you have to specify the font size both for Gnuplot and for Latex. Gnuplot may base its calculation on a different font than is actually used by Latex. To compensate for that, the point sizes you pass to each may have to be different (as they are in the below example). In order not to complicate things further, I would stick with scale=1 for including the generated plot. You can always tell Gnuplot to draw a smaller or larger plot using set size.

\documentclass[8pt,a4paper,dvipsnames]{article}
\usepackage[utf8]{inputenc}
\usepackage[left=2cm,right=2cm,top=1.5cm,bottom=1.5cm]{geometry}

\usepackage{gnuplottex}
\begin{document}

\begin{figure}[htp]
    \centering
    \fontsize{13}{16}\selectfont
    \begin{gnuplot}[scale=1, terminal=epslatex, terminaloptions={color dashed font ",16"}]
        set samples 50000
        set grid
        set key box
        set xrange [-3:1]
        set yrange [-5:30]
        set size 1.2, 1.2

        p x**2
    \end{gnuplot}
    \caption{parabolic curve} \label{fig:Parab}
\end{figure}

\end{document}