Guides · 6 min read
How to write alt text for equations
Alt text for an equation should say the equation the way you would read it aloud: every symbol named, the structure unambiguous, in a sentence or two. Where you can, publish the equation as real maths markup instead of an image, so that assistive technology reads it directly. This guide covers both, with worked examples and a free converter from LaTeX to spoken English.
Updated 11 November 2026
Markup first, images second
An equation written in MathML, or typeset on the page by MathJax, keeps its structure. A screen reader can speak it, a braille display can show it, a reader can enlarge it without blur and step through it term by term. An image of an equation can do none of that, whatever its alt text says.
- On the web: write LaTeX and render it with MathJax or KaTeX, which produce accessible output, or use MathML directly.
- In Word and PowerPoint: use the built-in equation editor, not a pasted picture.
- In PDFs: tag the document and give each equation alternative text, or better, also publish an HTML version.
Images of equations still turn up in slides, scanned handouts and older course material. For those, the Web Content Accessibility Guidelines require a text alternative (success criterion 1.1.1, non-text content, level A), and the rest of this guide is about writing a good one.
The rules for wording
- Write it as you would say it to someone who cannot see the board. “x squared plus y squared equals r squared”, not “equation 3”.
- Spell out operations and Greek letters: “plus or minus”, “the square root of”, “sigma”. Numerals can stay as numerals.
- Mark where groups begin and end. A listener cannot see a fraction bar or brackets, so say “the quantity … all over …” and “the sum from i equals 1 to n of”.
- Keep the order a reader would write it in, left to right, so it can be taken down as dictation.
- Keep it short. One equation is one or two sentences. A derivation belongs in the body text, with the alt text pointing to it.
- Do not start with “image of” or “equation showing”. The screen reader already announces an image.
Worked examples
| Equation | LaTeX | Alt text |
|---|---|---|
| Quadratic formula | x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} | x equals the quantity negative b plus or minus the square root of the quantity b squared minus 4 a c, all over 2 a |
| Bayes' theorem | P(A \mid B) = \frac{P(B \mid A) P(A)}{P(B)} | P of A given B, equals the quantity P of B given A, times P of A, all over P of B |
| Sample mean | \bar{x} = \frac{1}{n} \sum_{i=1}^{n} x_i | x bar equals 1 over n times the sum from i equals 1 to n of x sub i |
| Definite integral | \int_0^1 x^2 \, dx = \frac{1}{3} | the integral from 0 to 1 of x squared d x equals one third |
| Least squares | \hat{\beta} = (X^\top X)^{-1} X^\top y | beta hat equals X transpose X, inverse, times X transpose y |
| Euler's identity | e^{i\pi} + 1 = 0 | e to the power i pi plus 1 equals 0 |
Convert LaTeX to alt text
- Open the LaTeX to speech converter. It is free and needs no account.
- Paste the equation's LaTeX. The spoken form appears as you type.
- Copy it, and paste it as the image's alt text or the equation's description.
- Read it once against the equation. Check anything the context decides, such as whether a bar means “given” or “absolute value”.
Test it
Read the alt text to a colleague who has not seen the equation and ask them to write it down. If they write the same equation, the alt text works. If they have to ask where the fraction ends, add the grouping words.
Questions
Do the accessibility guidelines require alt text for equations?
Yes, when the equation is an image. WCAG success criterion 1.1.1 requires a text alternative that serves the same purpose for all non-text content. An equation in MathML is not an image and does not need alt text.
Should alt text be written in LaTeX?
Usually not: a screen reader reads LaTeX character by character. The exception is an audience that knows LaTeX well, such as mathematics researchers, for whom the source can be the most precise alternative. For everyone else, use words.
How long can alt text for an equation be?
As long as the equation needs, but one or two sentences is the practical limit for comfortable listening. For anything longer, describe the equation in the body text and keep the alt text brief.
What about a whole book of equations with no alt text?
That is the case Aethel is built for: it rebuilds the equations in a PDF or EPUB and reads the whole text aloud, equations included. See listening while you read.