lecture.studio

Math in Marp slides: KaTeX, MathJax and the syntax

By Ekrem Çetinkaya · Published

Marp renders LaTeX math out of the box: $E = mc^2$ inline and $$ … $$ for a display equation, with math: mathjax or math: katex in the front matter choosing the engine. Marp Core has used MathJax by default since version 3.0 (November 2021); KaTeX is lighter and faster in the preview. Both export to PDF through marp-cli and to PPTX as rendered images.

This guide covers the syntax, the engine choice, multi-line equations, macros for notation you use every week, sizing, and the checks that catch a broken formula before the lecture.

The syntax

---
marp: true
math: mathjax
---

# Expected waiting time

Inline: the mean is $\mu = \frac{1}{n}\sum_{i=1}^{n} x_i$.

Display:

$$
W_q = \frac{\lambda}{\mu(\mu - \lambda)}
$$

Inline math sits in a sentence; display math gets its own line, centred. Leave a blank line before and after a $$ block so the Markdown parser does not fold it into a paragraph.

KaTeX or MathJax?

KaTeX MathJax
Speed in the preview faster slower on long decks
Coverage most of LaTeX math more environments and packages
Default in Marp Core up to v2 since v3.0 (2021)
Set with math: katex math: mathjax

For a lecture deck either works; start with the default and switch only if a construct fails to render. math: false turns math off for a deck that uses dollar signs literally.

Aligned and multi-line equations

$$
\begin{aligned}
T_{\text{turnaround}} &= T_{\text{finish}} - T_{\text{arrival}} \\
T_{\text{waiting}} &= T_{\text{turnaround}} - T_{\text{burst}}
\end{aligned}
$$

aligned lines up on & and breaks on \\. Number equations by hand (\tag{1}) if the room will refer to them; automatic numbering is not a Marp feature.

Macros for the course's notation

Notation that appears every week (a vector style, an operator name) belongs in a macro, not retyped:

$$
\newcommand{\vect}[1]{\mathbf{#1}}
\newcommand{\E}{\operatorname{E}}
$$

Both engines accept \newcommand inside a math block. Whether a definition made on slide 2 is still known on slide 30 depends on the engine and the version, so define the macros once in a block on the first slide and check the last slide that uses them in the preview.

Sizing and layout

Math inherits the slide's font size. For a slide whose point is one equation, a scoped style enlarges it:

<style scoped>
section { font-size: 32px; }
</style>

For a deck-wide change, target the engine's container in the theme or the front-matter style: block: .katex { font-size: 1.1em; } for KaTeX, mjx-container { font-size: 110%; } for MathJax. Long equations do not wrap; split them with aligned rather than shrinking the font below what the back row can read.

Before the lecture: three checks

  1. Every formula renders in the preview. A missing brace shows as raw dollar signs or red text; scan the slide rail rather than paging through.
  2. The PDF matches. marp deck.md --pdf renders with the same engine; check the equation slides, since a font or a package difference shows up there first.
  3. Speaker notes carry the source. The derivation's textbook page in the note under the slide answers "where does this come from?" faster than re-deriving.

In Lecture Studio

The Marp preview in Lecture Studio renders math when the front matter has the math directive (math: mathjax is what the app's docs show), and the Check slides scan flags an overflowing equation slide. A deck the assistant writes from a paper cites the equation's source under the slide, which is the third check above done for you. PDF export is marp-cli's job, not the app's. The app runs on macOS 15 or later and needs an Oberik project key for the assistant.

FAQ

How do I write equations in Marp?

$…$ for inline math and $$…$$ on its own lines for display math, with math: mathjax or math: katex in the front matter.

Does Marp use KaTeX or MathJax?

Both are supported. Marp Core defaults to MathJax since version 3; set math: katex to use KaTeX instead.

How do I align multi-line equations in Marp?

Use \begin{aligned} … \end{aligned} inside a $$ block, with & at the alignment point and \\ between lines.

Do equations survive export to PDF and PowerPoint?

Yes. marp-cli renders them into the PDF; the default PPTX export includes them as part of the slide image. The editable PPTX mode does not keep them as equations.

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