Blog · Typography & Research
Line and letter spacing for dyslexia — what actually helps
Most conversations about dyslexia-friendly reading focus on font choice. That's reasonable — the font is the most visible thing. But once you've picked a reasonable typeface, the settings that tend to move the needle most are the ones almost nobody changes: line height and letter spacing. The research on both is specific enough to give concrete numbers. Here's what it says.
Why spacing matters more than many readers expect
The visual system doesn't read letter by letter. It samples patches of text, suppresses irrelevant detail, and reconstructs meaning from partial information. For that process to work, the letters in each word need to be distinct enough from their neighbours — both the letters beside them on the same line and the lines above and below.
Dyslexic readers are more sensitive to a phenomenon called crowding: the way nearby characters degrade each other's legibility at the edges of the visual field. When crowding is severe, the eye can see a letter clearly when it fixates directly on it, but the letters in peripheral vision — the ones it's about to land on in the next saccade — appear blurred, merged, or confused. Extra spacing reduces crowding. It gives each character more room to be perceived distinctly before the eye arrives.
This is separate from the question of which typeface to use. You can apply the same spacing improvements to OpenDyslexic, Atkinson Hyperlegible, Lexend, or any other font — and they compound. A good font with generous spacing is substantially easier to read than either improvement alone.
Line spacing (line height, or "leading")
Line spacing — the vertical distance between baselines — is the single spacing dimension most likely to be set badly on the web. The CSS default line-height is normal, which browsers interpret as roughly 1.2 times the font size. At typical body text sizes (16–18px), that means around 19–22px between baselines. For many readers that's adequate. For dyslexic readers, research suggests it falls short.
What the research says
Rello and Baeza-Yates published a study in 2013 that measured how text formatting variables affected reading speed and comprehension in dyslexic adults. Among the variables tested, line spacing had one of the clearest effects: participants read significantly faster — and with better comprehension — when line spacing was set to 1.4–1.5 times the font size compared with the typical default of 1.2. The gain came not from reading faster per line but from spending less time re-fixating: tighter line spacing caused the eye to accidentally land on the wrong line and then backtrack to find its place. More space between lines simply made it harder to lose track of where you were.
The British Dyslexia Association's Style Guide recommends a line height of at least 1.5 for any text intended for dyslexic readers, and describes anything below 1.4 as likely to cause reading difficulties. The WCAG 2.1 accessibility guidelines echo this with their Success Criterion 1.4.12 (Text Spacing), which states that content should not lose function when line height is set to 1.5 times the font size.
The upper limit matters too. Above about 2.0 times the font size, readers start losing the visual connection between lines. The paragraph stops feeling like a unit and the eye has to do extra work to locate the start of the next line. In practice, the useful range is somewhere between 1.5 and 1.9 for body text, with 1.6–1.7 being a reliable sweet spot for long-form reading.
Reading paragraph after paragraph of text with a line height this compressed is tiring. The lines sit close enough that the eye occasionally fixates on the wrong one. After a few hundred words, the effort starts to show up as fatigue rather than confusion — you may not know the spacing is the cause.
With a modest increase in line height, the same paragraph feels substantially more relaxed to read. Each line has room to breathe. The eye can jump from the end of one line to the start of the next without risk of landing on the wrong one, and the paragraph still coheres as a unit.
Practical recommendation
For body text on a screen: aim for line-height: 1.6 to 1.7. If you're reading on a site that feels cramped, that's probably the first number to increase. At 1.5 you're meeting the accessibility baseline. At 1.6–1.7 you're in the range most dyslexic readers find comfortable. Past 1.9 you're likely making things harder again.
If you experience reading fatigue — that specific tiredness that kicks in after a few paragraphs even when you understand the content — try increasing line height before reaching for a different font. It's one of the fastest single changes you can make.
Letter spacing (tracking)
Letter spacing — the horizontal distance between characters — has a more specific research foundation than any other typographic variable studied in the context of dyslexia. The key study is hard to dispute.
The Zorzi et al. 2012 study
In 2012, Marco Zorzi and colleagues at the University of Padova published a study in the Proceedings of the National Academy of Sciences testing whether extra letter spacing could reduce reading errors in children with developmental dyslexia. The study used a simple intervention: the same text was presented either in standard spacing or with letter spacing increased by approximately 2.5 times the default. No font was changed. No other variable was altered.
The results were striking. On average, reading errors dropped by around 20% in the extra-spacing condition. Reading speed, rather than falling as you might expect, was roughly maintained — children were not slower, just more accurate. The researchers attributed the effect to reduced crowding: the extra space reduced the extent to which neighbouring letters interfered with each other's perception at the edges of the visual field.
This is a real, peer-reviewed finding in a highly selective journal, and it has been replicated in several follow-up studies with broadly similar results. It's probably the strongest single piece of evidence that a typographic change — not a specialist font, just a CSS property value — can meaningfully improve reading accuracy for dyslexic readers.
The key number from Zorzi et al.: a letter-spacing increase of roughly 0.1 em (approximately 1.6px at 16px font size) produced the largest consistent gains. Larger increases had diminishing returns and occasionally broke word-shape recognition for faster readers who rely on holistic word forms rather than letter-by-letter decoding.
What letter spacing actually does
Standard body text on the web typically uses letter-spacing values between 0 and 0.02em. The increase tested in the Zorzi study — around 0.1em — is modest by design standards but perceptible: individual words look slightly more spread out, and dense paragraphs feel more open.
This is how most websites present their body text. The letters sit at the kerned spacing built into the typeface, which is usually optimised for print and tends to be slightly tighter than what dyslexic readers need on screen.
The same paragraph with a small letter-spacing increase. Individual characters are slightly more separated. If you have the specific crowding sensitivity that Zorzi's study identified, this is likely where you'll notice a difference. Words are still perceived as units.
The upper limit
More is not always better. Skilled readers — including many dyslexic adults who have developed strong reading strategies — rely partly on the overall shape of familiar words (the "word envelope") rather than reading each letter in sequence. That envelope breaks down when spacing gets too wide. At around 0.2em or beyond, common words start to look unfamiliar, and reading speed often drops even as accuracy stays stable or improves slightly. The Zorzi study found 0.1em was near the sweet spot; the BDA Style Guide suggests keeping letter spacing below 0.12em for body text.
This is also why some dyslexia-specific fonts — notably Dyslexie — build wider character spacing directly into the font metrics. They effectively bake in the Zorzi finding so you don't have to add letter-spacing manually. The tradeoff is that fonts with wide internal spacing look unusual in headings and short labels, where readers expect more compact letterforms. See our piece on x-height and letter design in dyslexia fonts for more on how letter geometry interacts with spacing.
Word spacing — the third dimension
Line height and letter spacing are the two variables with the best-controlled research behind them. Word spacing — the gap between words — also matters, but in a somewhat different way: rather than reducing crowding within a word, it helps the eye segment the text stream into discrete units. We have a dedicated piece on word spacing and dyslexia that covers the research and practical values in detail.
The short version: word spacing of around 0.2–0.35em above the default tends to help readers who frequently lose their place or read words together. It interacts with letter spacing — if you increase letter spacing substantially, the visual distinction between intra-word spacing and inter-word spacing shrinks, so you often need to increase word spacing at the same time to preserve word boundaries.
The problem with too much of everything
A natural response to reading this is to set every spacing value to its maximum. The evidence argues against that. Spacing adjustments help by reducing crowding and making the page easier to parse. But the reading system also relies on relationships — between letters within a word, between words within a line, between lines within a paragraph. Push every dimension too wide and those relationships start to break: words look like random strings of letters, lines look unconnected, the paragraph loses its visual integrity as a unit.
There's also an interaction with font choice. Fonts with generous built-in spacing (Lexend, Atkinson Hyperlegible, and their relatives) already start further along the spacing continuum than, say, Times New Roman. Adding the same letter-spacing increment to Lexend as you'd add to Times pushes Lexend past the useful range. Start with smaller adjustments when using a font already designed for readability. See our dyslexia-friendly web design checklist for how this applies to website typography more broadly.
A practical starting-point template
If you're building a reading environment — whether in a browser extension, a note-taking app, or your own reading setup — these values work well as a starting point for most dyslexic readers:
| Property | Starting value | Range to experiment in |
|---|---|---|
| line-height | 1.6 | 1.5 – 1.9 |
| letter-spacing | 0.06em | 0.04em – 0.12em |
| word-spacing | 0.1em | 0.05em – 0.3em |
| font-size (body) | 17–18px | 16–22px |
| max-width (line length) | 65–70ch | 55–80ch |
Adjust from there based on your own reading. The most useful test is to take a long article you actually want to read, set these values, and then read it for ten minutes before adjusting anything. Brief exposure rarely reveals how a setting feels at sustained reading length — most spacing problems announce themselves as fatigue or eye strain rather than immediate discomfort.
How to apply these settings in Chrome today
Very few websites use line heights above 1.5 or any positive letter-spacing. The default web is, by these numbers, typographically cramped for dyslexic readers.
Browser reader modes (Safari's Reader View, Firefox's Reader Mode) typically do improve line height, but they strip out the styling you may want and they don't work on all pages. Reader mode versus reading extensions covers the tradeoffs.
The most reliable method is a font-override extension that also controls spacing. LexiFont applies your choice of dyslexia-friendly typeface across every website, and LexiFont Pro extends this with custom line-height and letter-spacing controls — so you can set values once and have them apply everywhere, including on sites with tightly controlled CSS that would otherwise override your adjustments.
If you already have LexiFont and haven't yet tried tuning the spacing sliders, the line-height control is the fastest single improvement. A session of reading at 1.65 line height compared to the web's typical 1.2–1.3 defaults is usually enough to make the value of the change obvious.
What different fonts do by default
Not all fonts start from the same spacing baseline, and this affects how much you need to add manually.
Lexend was designed explicitly to reduce visual stress: it uses wider letter-spacing than most fonts at equivalent sizes. At its default metrics, it's already closer to the Zorzi sweet spot than most system fonts. Adding further letter-spacing to Lexend has diminishing returns sooner than it does with tighter fonts.
Atkinson Hyperlegible uses generous spacing too, though it prioritises character distinctiveness (unique letterforms) over broad tracking. It benefits more from line-height increases than letter-spacing increases.
OpenDyslexic has its own internal spacing baked into the font, wide enough that many readers don't need further tracking adjustments. The dominant spacing variable with OpenDyslexic is usually line height — its letterforms are generous in width, and the heavy weighted bottoms can feel crowded vertically if line height is too tight.
System fonts like Arial, Georgia, and Calibri all start from tighter defaults and benefit most from both increases. If you're reading an unmodified site in a standard system font, the jump from its default spacing to the values in the template above will typically be the largest perceptible improvement. See our guide to changing the font on any website in Chrome if you want to start there.