Capital chapter names in book class

Question

In the book documentclass how can you make the chapters be in capital letters?

For example:

Chapter 1 --> CHAPTER 1

etc...

Answer 1

The book document class has a low-level macro named \chaptername, but what's used in the typesetting of chapter headers is \@chapapp. It's best to leave \chaptername alone and modify \@chapapp, by applying (a) \MakeUppercase to its argument and (b) a modest amount of letter-spacing to the all-caps string; without some letter-spacing, strings of all-caps letters can easily look very "blocky" and dense.

\documentclass{book}
\usepackage{microtype} % for '\textls' macro

\makeatletter % default is "\newcommand\@chapapp{\chaptername}"
\renewcommand\@chapapp{\textls[40]{\MakeUppercase{\chaptername}}}
\makeatletter

\begin{document}
\chapter{Good morning}
\end{document}

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Addendum: If your document has one or more chapter-level appendices, and assuming you'll want the prefix string "Appendix" to be converted to uppercase letters as well, you will need to provide the following instructions after \appendix:

\makeatletter 
\renewcommand\@chapapp{\textls[40]{\MakeUppercase{\appendixname}}}
\makeatletter

Answer 2

A low level way of doing this is to simply have

\renewcommand\chaptername{CHAPTER}

In your preamble:

\documentclass{book}

\renewcommand\chaptername{CHAPTER}

\begin{document}

\chapter{Hello World}

\end{document}