# amsbook does not adapt chapter title size to scrextend

If one changes the text size in an amsbook style, chapter titles' text size does not adapt to this, and then looks smaller than intended. How can this be fixed?

\documentclass[fleqn,a4paper, 12pt, twoside]{amsbook}
\usepackage[
top = 0.5 in,
bottom = 1 in,
left = 0.5 in,
right = 0.5 in]{geometry}

\usepackage[fontsize=15pt]{scrextend}
\usepackage[utf8x]{inputenc}
\usepackage{amsfonts,amssymb,amsmath}
\usepackage{lipsum}

%\renewcommand{\thechapter}{\Roman{chapter}}

\begin{document}
\frontmatter

\chapter{A title too small}

\lipsum[1]

\end{document}


There is a very silly "fix" to this which is adding \Large inside the title name, but this ruins headers and TOCs.

• The class has \fontsize{\@xivpt}{18}\bfseries, independently of the main font size. Mar 15 '18 at 16:43

The class hardwires 14.4pt font size for the chapter title.

You can change it by patching the relevant command, but don't forget to load fix-cm (or a scalable font package).

\RequirePackage{fix-cm}
\documentclass[fleqn,a4paper, 12pt, twoside]{amsbook}
\usepackage[
top = 0.5 in,
bottom = 1 in,
left = 0.5 in,
right = 0.5 in]{geometry}

\usepackage[fontsize=15pt]{scrextend}
\usepackage[utf8]{inputenc}
\usepackage{amsfonts,amssymb,amsmath}
\usepackage{etoolbox}

\usepackage{lipsum}

\makeatletter
{\fontsize{\@xivpt}{18}}
{\Large}
{}{}
{\fontsize{\@xivpt}{18}}
{\Large}
{}{}
\makeatother

%\renewcommand{\thechapter}{\Roman{chapter}}

\begin{document}
\frontmatter

\chapter{A title too small}

\lipsum[1]

\end{document}


• @PedroTamaroff You're welcome! Mar 15 '18 at 17:06