How to Set a 13pt Font in the Memoir Class

The memoir class does not provide a built-in 13pt class option. If you write \documentclass[13pt]{memoir}, LaTeX may report that the option is unused and fall back to the class’s default size.

To get 13pt text, load memoir with a supported class size and use the fontsize package to set the document’s nominal size. Here is a minimal example:

\documentclass[12pt]{memoir}
\usepackage[fontsize=13pt]{fontsize}

\begin{document}
This body text is set at a nominal size of 13 points.

\section{A section}
The section heading uses the class's heading style.
\end{document}

What the package changes

The fontsize package changes the document’s base font size and adjusts the standard size commands—such as \small, \normalsize, and \large—around that base. This is more consistent than changing the font size for one paragraph only.

The example uses the package’s default baseline spacing. Font size and baseline spacing are different: 13pt describes the size of the characters, while the baseline skip is the distance between successive text baselines. If you need to control line spacing too, consult the package documentation for its baselineskip option and choose a value appropriate to your font and layout.

Why not use \fontsize alone?

A command such as

\fontsize{13pt}{15.6pt}\selectfont

sets the size and baseline skip for the current font selection. It can be useful for a specific block, but by itself it does not redefine the document’s standard size commands. Later commands or environments that select \normalsize or another size can therefore use the class’s original size settings. Use the package approach when you want 13pt to be the document-wide base size.

Common mistakes

• Passing 13pt as a memoir option: memoir’s built-in size choices do not include 13pt. Use a supported option such as 12pt or 14pt as the class size, then set 13pt with the package.
• Changing only one paragraph: \fontsize applies to the current font selection, not automatically to every part of the document.
• Assuming 13pt also determines line spacing: the baseline skip is a separate setting. Check the compiled pages, especially if the document must meet a particular layout specification.
• Expecting every element to look exactly 13pt: headings, captions, footnotes, and other elements may intentionally use different sizes as part of memoir’s formatting. The package changes the standard size scale, but those elements can still have their own styles.