Default Merriweather font size is too large

Question

I would like to use Merriweather as my serif font but the default font size is too large and it makes the document look out of balance.

How can I make Merriweather smaller so that it fits better with other fonts? I don't want to scale all fonts (using relscale) because this would still not balance the fonts. If I make the sans-serif font larger, the footnotes and image captions are still bad.

Below is the sample document I'm using.

\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{amsmath,amssymb}

% comment out this line to remove Merriweather
\usepackage{merriweather}

\usepackage{titlesec}
\titleformat*{\section}{\bfseries\Large\sffamily}
\titleformat*{\subsection}{\bfseries\large\sffamily}
\titleformat*{\subsubsection}{\bfseries\normalsize\sffamily}

\usepackage{hyperref}
\usepackage{lipsum}
\usepackage{microtype}

\title{Fonts for \LaTeX}

\begin{document}

\maketitle

\section{Section}

\lipsum[1]


Inline Math $x=4$ more text. An inline link \url{https://www.gogole.com}.

\begin{displaymath}
\Delta G^{\circ}= -R\,T\ln \dfrac{[S_1][S_2]}{[S_1S_2]}.
\end{displaymath}

Some text \texttt{Hello World} and more\footnote{A footnote to test the font size of footnotes.}. 

\subsection{Subsection Title}

\lipsum[2]

\subsubsection{Subsubsection Title}

\lipsum[3]

\end{document}

With Merriweather:

Default font:

With libertine:

Answer 1

There is no option to scale the serif font, the scale option scales only the sans serif, but you can redefine the internal scale command:

\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{amsmath,amssymb}

% comment out this line to remove Merriweather
\usepackage[]{merriweather}

\usepackage{titlesec}
\titleformat*{\section}{\bfseries\Large\sffamily}
\titleformat*{\subsection}{\bfseries\large\sffamily}
\titleformat*{\subsubsection}{\bfseries\normalsize\sffamily}

\usepackage{hyperref}
\usepackage{lipsum}
\usepackage{microtype}

\title{Fonts for \LaTeX}

\makeatletter
\renewcommand\Merriweather@scale{0.5} %adapt to your liking
\makeatother
\begin{document}

\maketitle

\section{Section}

\lipsum[1]


Inline Math $x=4$ more text. An inline link \url{https://www.gogole.com}.

\begin{displaymath}
\Delta G^{\circ}= -R\,T\ln \dfrac{[S_1][S_2]}{[S_1S_2]}.
\end{displaymath}

Some text \texttt{Hello World} and more\footnote{A footnote to test the font size of footnotes.}.

\subsection{Subsection Title}

\lipsum[2]

\subsubsection{Subsubsection Title}

\lipsum[3]

\end{document}

Answer 2

I decreased the font to 10 pt and slightly increased the character of the mathematical font. I hope it's okay. See also this link: http://www.ctex.org/documents/packages/special/moresize.pdf to page 5.

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{amsmath,amssymb}

% comment out this line to remove Merriweather
\usepackage{merriweather}

\usepackage{titlesec}
\titleformat*{\section}{\bfseries\Large\sffamily}
\titleformat*{\subsection}{\bfseries\large\sffamily}
\titleformat*{\subsubsection}{\bfseries\normalsize\sffamily}
\usepackage{hyperref}
\usepackage{lipsum}
\usepackage{microtype}
\makeatletter
\DeclareMathSizes{\@xipt}{\@xiipt}{12}{14}
\makeatother


\title{Fonts for \LaTeX}

\begin{document}

\maketitle

\section{Section}

\lipsum[1]


Inline Math $x=4$ more text. An inline link \url{https://www.google.com}.

\begin{displaymath}
\Delta G^{\circ}= -R\,T\ln \dfrac{[S_1][S_2]}{[S_1S_2]}.
\end{displaymath}

Some text \texttt{Hello World} and more\footnote{A footnote to test the font size of footnotes.}. 

\subsection{Subsection Title}

\lipsum[2]

\subsubsection{Subsubsection Title}

\lipsum[3]

\end{document}