Blog · Typography
Line spacing and letter spacing for dyslexia - what actually matters
When people talk about dyslexia-friendly reading, the conversation almost always turns to fonts. OpenDyslexic, Lexend, Atkinson Hyperlegible. But there's a quieter intervention with stronger evidence behind it: simply pushing the letters and lines further apart. The peer-reviewed gain from extra letter spacing is, in some studies, larger than the gain from changing fonts at all.
The short answer
Letter spacing is the high-value lever. A 2012 PNAS study by Zorzi and colleagues showed that increasing letter spacing by roughly +2.5 points (about +14% of the character width) doubled reading speed for dyslexic children, with a parallel drop in error rate. The effect held for both Italian and French readers. No font change was involved.
Line spacing matters too, but in a softer way. Generous line height (around 1.5 to 1.8) reduces line-skipping and visual fatigue, but the speed gains are smaller and less consistent in the literature.
Word spacing is the under-discussed third. Slightly wider spaces between words help some readers more than letter spacing alone, especially in heavily kerned modern fonts.
Why spacing matters at all
Reading is not a smooth glide along the page - it is a sequence of short eye jumps called saccades, separated by fixations of about 200-250 milliseconds. For a fluent reader, each fixation captures a small window of letters (the "perceptual span") and the eye moves on. For a dyslexic reader, two things go wrong more often than they should: adjacent letters interfere with each other's recognition (a phenomenon called crowding), and the eye sometimes lands in the wrong place, requiring a corrective regression back along the line.
Both of these problems are made worse by tight spacing. When letters sit close together, crowding increases and individual glyphs are harder to identify. When lines sit close together, the eye has more chances to drop down to the wrong line on the return sweep. Pushing things apart - letters, words, lines - reduces both error modes. It does not fix dyslexia, but it gives the visual system more room to do its work.
The research on letter spacing
The strongest piece of evidence is Zorzi et al. (2012), Extra-large letter spacing improves reading in dyslexia, published in PNAS. The study tested 74 dyslexic children aged 8 to 14 across two countries. Each child read two matched passages, one set in default spacing and one in extra-wide spacing. The wide-spacing condition produced a near-doubling of reading speed and a roughly 50% drop in errors. Crucially, the effect was much larger in dyslexic readers than in their non-dyslexic peers, suggesting the intervention is genuinely targeted rather than a general reading-comfort boost.
Why such a large effect? The leading explanation is that crowding is disproportionately worse in dyslexia. Italian and French researchers had been describing this pattern - poor reading specifically in close-set type - for years before Zorzi's group ran the formal study. The fix is mechanically simple: separate the letters, and the visual system has less interference to fight through.
Subsequent work has been broadly supportive but more nuanced. The benefit appears stronger in shorter words, in less-skilled readers, and in fonts with already-tight default kerning. It also seems to interact with letter shape - when letters are visually similar (a, e, o, c) the spacing benefit is larger because crowding is the dominant problem. For more on disambiguating similar shapes through font choice, see our piece on Atkinson Hyperlegible in the browser.
You can see why "airy" is rarely the default - it consumes screen real estate. But for dyslexic readers, the trade is often worth it.
The research on line spacing
Line spacing has a smaller and less unanimous evidence base than letter spacing. Most published studies on dyslexia and line spacing find a comfort and accuracy benefit, with a small or null effect on reading speed. The mechanism is different: where letter spacing helps within-line recognition, line spacing helps between-line tracking - the moment when your eye finishes a line and has to find the start of the next one.
If you have ever found yourself accidentally re-reading the same line, or skipping a line entirely, that's a tracking failure. Wider line spacing reduces it. So does shorter line length: a tightly-spaced line of 100 characters is harder to track than a generously-spaced line of 60. This is why reading rulers, finger-tracking, and reader-mode columns all have a real (if modest) effect even before you change a single font.
The practical sweet spot for dyslexic readers tends to be a line height of about 1.5 to 1.8 times the font size. Below 1.4, lines start to feel cramped. Above 2.0, the page starts to feel like a checklist - the lines feel disconnected from one another, and prose loses its flow. 1.5 is the value the British Dyslexia Association recommends in its style guide, and it's a sensible default.
Word spacing - the quiet third lever
Word spacing gets less attention than letter or line spacing, but it can produce noticeable gains for readers who find words "running together." Modern body fonts are often designed for density - news sites and content management systems frequently set word spacing slightly tight to fit more text per screen. The default browser word-spacing is fine for fluent readers, but for dyslexic readers, an extra 5-10% can produce a real comfort improvement without making the page feel weird.
The CSS property is simply word-spacing. Values of 0.05em to 0.1em are usually enough. Anything beyond that starts to create rivers of white space inside paragraphs, which is its own readability problem.
The numbers that actually work
For someone setting up a dyslexia-friendly reading environment, here are the values that are well-supported by both research and reader reports:
| Property | Value | Why |
|---|---|---|
| font-size | 16-19 px | Below 14 px crowding worsens; above 20 px line-tracking suffers |
| line-height | 1.5 to 1.8 | Reduces line-skipping; British Dyslexia Association recommends 1.5 |
| letter-spacing | +0.05em to +0.1em | Mitigates crowding; Zorzi 2012 used roughly +0.14em equivalent |
| word-spacing | +0.05em to +0.1em | Helps when words feel run together; small effect but cheap to add |
| max line length | 60-70 characters | Reduces tracking failures on the line return |
| paragraph spacing | 1em or more | Visual breathing room between blocks of text |
None of these are exotic - they're the same defaults you'll find recommended for accessibility in WCAG 2.1 success criterion 1.4.12 (Text Spacing), which any modern site is supposed to support without breaking layout.
How to apply these to any website
The trouble is that most websites do not actually use these values. News sites, blogs, and especially documentation sites tend to default to line-height 1.4 or lower and zero letter spacing. Reader mode (built into Safari, Firefox, and most browsers) is the simplest fix - it strips the page down to a clean column with sensible spacing. For more on when reader mode helps and when a dedicated extension does, see our comparison of five ways to change fonts on any website in Chrome.
For more control, three approaches work:
Browser-wide CSS via a user stylesheet. Tools like Stylus let you apply CSS to every site you visit. A sensible starter rule:
body, p, li, article, main {
line-height: 1.6 !important;
letter-spacing: 0.05em !important;
word-spacing: 0.05em !important;
}This is heavy-handed (the !important overrides site styles) and will occasionally break a fragile layout, but it works on the long tail of sites that ignore reading defaults.
A dedicated accessibility extension. LexiFont handles font, line spacing, letter spacing, and word spacing as separate sliders, applied to every site automatically. The free tier covers the basics; LexiFont Pro adds the full set of dyslexia fonts (OpenDyslexic, Lexend, Atkinson Hyperlegible, Comic Neue) so you can pair spacing changes with a font change in one click.
Reader mode + zoom. If you don't want any extension, opening reader mode and bumping the browser zoom to 110-125% will get you most of the way there. The line-height in most reader modes is already around 1.5, and zooming widens letter spacing proportionally. It's a perfectly reasonable starting point.
Combining spacing with a dyslexia font
A reasonable question: if I switch to a font designed for dyslexia, do I still need the spacing tweaks? The answer is yes, mostly. Dyslexia fonts solve a different problem (letter shape disambiguation) from spacing tweaks (crowding and tracking). They are additive rather than redundant.
The one font that does some of the spacing work for you is Lexend - it ships with hyper-expanded letter and word spacing baked into the font metrics. If you set Lexend as your reading font, you can leave letter-spacing at zero and still get most of the crowding benefit. See our deep dive on Lexend for more. For OpenDyslexic, the letter shapes are unusual but the spacing is conventional, so the tweaks above still apply.
If you're choosing between a font change and a spacing change as a starting point, start with spacing. It's reversible, it doesn't change the visual character of the page, and the evidence base is stronger. If spacing alone doesn't get you to comfortable reading, layer a font change on top. Our 2026 review of dyslexia fonts walks through the options.
The trade-offs to be honest about
Wider spacing is not free. Three real costs:
Vertical real estate. Line-height 1.8 means a passage that fit on one screen now takes 1.5 screens. On a phone, this can mean significantly more scrolling. Most readers adapt quickly, but it's worth noting.
Layout breakage. Some sites pin elements to specific pixel positions and don't accommodate larger spacing values. You'll occasionally see overlapping text or buttons that bleed into headlines. This is the site's fault under WCAG 1.4.12, but it's a real-world friction.
Aesthetic mismatch. Body copy at letter-spacing 0.1em looks subtly off to typographically-trained eyes. If you read for pleasure as well as function, you may find some long-form sites less satisfying with heavy spacing. Many readers run a "reading profile" with heavy spacing and a separate "browsing profile" closer to default - it's a sensible workflow.
What to try first
If you're starting from scratch and want a single thing to test, set letter-spacing to 0.06em on body text and read for an hour. Most readers who are going to benefit notice it inside the first paragraph. If it helps, layer line-height 1.5 and word-spacing 0.05em on top. If it doesn't, try a dyslexia font instead - the people who don't respond to spacing often respond strongly to letter-shape changes, and vice versa.
If you're already running a dyslexia font and still finding reading effortful, the most likely missing piece is spacing. It's the cheapest and most reversible thing to try, and the evidence behind it is, ironically, stronger than the evidence behind any specific font choice.
Get LexiFont Pro - dyslexia fonts and spacing controls in one extension, $14.99 one-time
Further reading
- Best fonts for dyslexia in 2026 - a research-first guide
- Lexend in Chrome - reading-speed research and how to apply it
- Atkinson Hyperlegible - letter-shape precision for low vision
- Five ways to change fonts on any website in Chrome
- Irlen syndrome and tinted overlays for screen reading
- Bionic Reading vs OpenDyslexic - a comparison