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Dyslexia-Friendly Fonts: What the Research Actually Says

OpenDyslexic, Lexend and Atkinson Hyperlegible checked against the studies, and why spacing and text size matter more than the font itself.

Productivity··10 min read

Search for "dyslexia font" and you'll find typefaces with heavy, bottom-weighted letters, fonts that promise better reading fluency, and plenty of confident advice. The research is less exciting, and more useful. In controlled studies, specially shaped fonts mostly don't help. What does seem to help is more room: bigger text, wider gaps between letters and words, and a font that keeps similar letters apart.

This post goes through the main fonts one at a time, then the spacing and size findings, and ends with how to set all of it up on Binary Decimal.

OpenDyslexic: weighted letters, no measurable gain

OpenDyslexic is a free, open-source font. Its own README describes the idea: heavier bottoms on letters to signal which way up they are (so b, d, p and q are easier to tell apart), longer ascenders and descenders, bolder punctuation, and wider letter and line spacing.

It has been tested directly. In a 2016 study in Annals of Dyslexia, Jessica Wery and Jennifer Diliberto had 12 students with dyslexia, aged 9 to 12, name letters, read real words and read nonsense words in OpenDyslexic, Arial and Times New Roman. OpenDyslexic didn't improve reading speed or accuracy, for any student or for the group as a whole, and none of the students said they preferred it.

A larger eye-tracking study by Luz Rello and Ricardo Baeza-Yates (2016) had 97 people, 48 of them with dyslexia, read on screen in 12 fonts. OpenDyslexic didn't make reading better or worse for the dyslexic group, and both groups preferred ordinary fonts like Verdana and Helvetica to it.

If you like how it looks, that's a fair reason to use it. It just isn't a treatment.

Dyslexie: the benefit was the spacing

Dyslexie is a font created in 2008 by Dutch artist Christian Boer, with a similar idea of distinct, weighted letter shapes. The study that explains the most about "dyslexia fonts" in general was done on this one.

Eva Marinus and colleagues (2016) found that children who were struggling readers read about 7% more words per minute in Dyslexie than in standard Arial. Then they gave Arial the same spacing between letters and words that Dyslexie has. The difference was no longer significant. The letter shapes weren't doing the work; the spacing was.

Sanne Kuster and colleagues (2018) then ran a bigger test in the Netherlands. In one experiment, 170 children with dyslexia read text in Dyslexie and in Arial; in a second, 102 children with dyslexia and 45 without read word lists in Dyslexie, Arial and Times New Roman. Dyslexie didn't make reading faster or more accurate in either experiment, and most children preferred Arial or Times New Roman.

Lexend: a promising claim, thin evidence so far

Lexend is a family of fonts created by educational therapist Bonnie Shaver-Troup. Its website describes the approach as a sans serif design with expanded letter shapes and very wide spacing, meant to reduce crowding, and it now ships as a free variable font.

The evidence offered for it comes from its creator. The Lexend site reports a trial with 20 third graders who read passages in Times New Roman and in four Lexend widths: the average went from 110 to 128 words correct per minute, and 17 of 19 children scored higher with Lexend. The site doesn't point to a peer-reviewed paper for this trial, and we couldn't find an independent replication.

There's also a design question in that comparison. Times New Roman is a narrow, tightly spaced serif font; Lexend is wide and generously spaced. Given what Marinus found with Dyslexie, a gain over Times New Roman may say more about spacing than about Lexend's letters. Lexend may well be comfortable to read; it just hasn't been shown to beat other well-spaced fonts.

Atkinson Hyperlegible: made for low vision

Atkinson Hyperlegible comes from the Braille Institute, released in 2019 and free to use. It was designed for readers with low vision, not for dyslexia, and the Braille Institute doesn't claim otherwise. Its focus is telling similar characters apart: B and 8, O and 0, and the capital I, lowercase l, lowercase i and the digit 1 all get clearly different shapes.

That helps anyone who misreads look-alike characters in numbers, codes and reference IDs. We know of no dyslexia study behind it, so try it and keep it if reading feels easier.

What actually helps: spacing

The strongest result in this area isn't about a font at all. In a 2012 study in PNAS, Marco Zorzi and colleagues tested 74 children with dyslexia aged 8 to 14, 34 reading Italian and 40 reading French. The same text was printed in 14-point Times with normal spacing, and again with 2.5 points of extra space between letters (with word and line spacing increased to match).

With the extra spacing, the children made far fewer errors; in a follow-up group, the spaced text produced less than half the errors of the normal text. Reading speed went up by about 0.3 syllables per second, which the authors note is about what Italian children with dyslexia typically gain in a whole school year. The explanation they give is crowding: letters packed close together are harder to recognise, and readers with dyslexia are affected by it more than other readers.

There's an important catch. Jessica Galliussi and colleagues (2020) tested 64 children with dyslexia and 64 without, varying letter shape and letter and word spacing separately. The letter shapes made no difference. Wider letter spacing on its own, without more space between words, slowed reading. Words need to stay visibly separate from each other.

The British Dyslexia Association's style guide reflects the same idea. Among its recommendations:

  • letter spacing of around 35% of the average letter width, and not so much that it hurts readability;
  • word spacing at least 3.5 times the letter spacing;
  • line spacing of about 1.5;
  • sans serif fonts such as Arial, Verdana or Calibri;
  • no italics or underlining for emphasis (use bold), and no continuous capitals;
  • left-aligned text, not justified.

What actually helps: size

Text size has the clearest effect after spacing. Rello and colleagues (2013) used eye tracking with 28 adults and teenagers with dyslexia reading Wikipedia articles at six sizes from 10 to 26 points, and four line spacings. Size changed readability and comprehension; line spacing, in that study, didn't. They recommended 18 points for screen text. A later study by Rello, Pielot and Marcos (2016) with 104 readers in general found the same pattern: readability and comprehension kept improving up to 18 points.

The BDA guide's baseline is 12 to 14 point, or 16 to 19 px on screen, and it notes that some dyslexic readers will want larger. In practice: if you're squinting, go up a step or two.

Line length and layout

Long lines make it harder to find the start of the next one. The W3C's accessibility guidelines (WCAG success criterion 1.4.8) ask that a reader can get blocks of text no wider than 80 characters, not justified, with line spacing of at least one and a half. WCAG 1.4.12 sets a related rule for designers: a page shouldn't break when a reader raises line height to 1.5 times the text size, letter spacing to 0.12 times, and word spacing to 0.16 times.

The fonts compared

Font Made for Evidence for dyslexia
OpenDyslexic Dyslexia (weighted, distinct letters) No gain in speed or accuracy (Wery & Diliberto 2016; Rello & Baeza-Yates 2016)
Dyslexie Dyslexia (distinct letters, wide spacing) Gains disappear when spacing is matched (Marinus 2016); no gain (Kuster 2018)
Lexend Reading fluency (wide, well spaced) The creator's own trial against Times New Roman; no independent replication found
Atkinson Hyperlegible Low vision (look-alike characters kept apart) Not tested for dyslexia that we know of
Your device's font Everyone Sans serif fonts read well on screen (Rello & Baeza-Yates 2016)

How to set this up on Binary Decimal

Every option is in Settings → Appearance. You can also open the same panel from the palette button in the header. Changes apply straight away, and they're saved in your browser (and in your backup and sync, if you use them). Nothing is sent anywhere.

  1. Font. Choose Default (your device's own font), Atkinson Hyperlegible, Lexend or OpenDyslexic. The fonts are hosted on our own site and only download once you pick one. OpenDyslexic is scaled down slightly so a line holds about as many words as it would in the default font. Code and maths keep their own fonts so they stay readable.
  2. Text size. Steps from 90% to 150%. This is the setting with the best evidence behind it, so start here.
  3. Line spacing. Normal, Relaxed (about 1.65) or Loose (about 1.9).
  4. Letter spacing. Normal, Wide or Wider. Both wider settings add space between words as well as letters, so words stay apart, which matters given the Galliussi result. Wider uses the WCAG 1.4.12 values: 0.12 of the text size between letters and 0.16 between words.
  5. Theme. If bright white is uncomfortable, Paper is a warm, off-white theme. The BDA guide suggests dark text on a light background that isn't pure white.

A sensible starting point: text size 120%, letter spacing Wide, line spacing Relaxed, and your device's font. Read a long page for a few minutes, then change one thing at a time so you can tell what helped.

The teleprompter also has its own text size and line spacing for reading to camera, and the Markdown editor has a preview for rereading longer notes once they're written.

Outside this site

Chrome has a built-in Reading mode: right-click a page and choose "Open in reading mode", or press Alt+Shift+R (⌘+Option+R on a Mac). Its settings let you change the font, font size, colour theme, line height and letter spacing for any article.

The short version

  • Specially shaped "dyslexia fonts" haven't beaten ordinary fonts in controlled studies. Where Dyslexie looked better, the spacing explained it.
  • Larger text and more space between letters and words are what the evidence supports.
  • Lexend's evidence is promising but comes from its creator. Atkinson Hyperlegible was made for low vision.
  • Pick the font you find comfortable, then spend your effort on size and spacing.
  • On Binary Decimal, it's all in Settings → Appearance.

Sources

dyslexiaaccessibilityfontsreadingproductivity

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