Blog · Typography
Line spacing and letter spacing for dyslexia — what actually matters
Most advice for dyslexic readers starts and ends with font choice. That's a mistake. The research is fairly clear that spacing — between lines, between letters, and between words — moves the needle at least as much as the typeface itself, and sometimes more. The good news is that spacing is something you can change on any website in about ten seconds. The less good news is that the optimum is narrower than the internet implies, and overdoing it makes reading worse.
The short answer
Start here: line-height around 1.5×, letter spacing (tracking) around +7%, word spacing around +15–20%. Those are the British Dyslexia Association's published numbers, and they're the closest thing the field has to a consensus baseline.
Then adjust by feel — tighter if the page starts to feel sparse and your eye has to leap, looser if letters feel mashed together. Don't go past 2× line-height or 0.2em letter spacing; the evidence on extreme values is much weaker than the marketing for "maximum-spacing" reading apps suggests.
Why spacing matters more than people think
Reading is not a smooth glide across a line of text. Your eye moves in jumps called saccades, fixating briefly on a point a few characters into each word, then leaping to the next. Between fixations, you take in a roughly 15–20 character window of useful information. The two things that most often go wrong for dyslexic readers happen at the edges of that window: crowding (the brain has trouble isolating one letter when neighbouring letters are too close) and line-tracking failure (the eye, returning from the end of one line to the start of the next, lands on the wrong line).
Both problems are spatial, not typographic. A different font alone won't fix them. More space between letters reduces crowding. More space between lines reduces tracking failure. That's why the most-cited interventions for dyslexic reading — going back to a 2012 PNAS paper by Zorzi and colleagues that's been replicated several times since — found that increased letter spacing alone produced reading-speed gains of roughly 20% in dyslexic children, with no font change at all.
The mechanism is straightforward: letters that are slightly further apart are easier to recognise as discrete shapes, and the brain spends less effort segmenting the visual stream into individual characters. That frees up cognitive resources for actually processing meaning, which is the part of reading dyslexia genuinely makes harder.
The three knobs
There are exactly three spacing parameters worth tuning. In CSS terms they map to line-height, letter-spacing, and word-spacing. In any browser extension that lets you override styles — including LexiFont — you'll see them under similar names.
1. Line height (leading)
This is the vertical distance between baselines of consecutive lines. A line-height of 1.0 means lines stack with no breathing room; 1.5 means there's half a line of empty space between each. It's the single most important variable for line-tracking failure.
The British Dyslexia Association's Dyslexia Style Guide recommends a minimum of 1.5× the font size, and the research broadly supports this. Below 1.4 the eye starts mis-landing on adjacent lines when sweeping back from the end of a row; above about 1.8 the lines feel disconnected and your eye has to work harder to find the next one. The sweet spot for most adult dyslexic readers is between 1.5 and 1.7.
2. Letter spacing (tracking)
This is the horizontal space added between every pair of letters within a word. The default for most fonts is whatever the type designer baked in (effectively zero extra). For dyslexic readers, adding a small positive amount — somewhere between +0.05em and +0.12em, or 5% to 12% of the font size — consistently improves reading.
Why such a narrow band? Because letter spacing is the variable where overshooting hurts most. Push it past about 0.15em and words start to dissolve into separate letters. Your brain stops recognising the word shape and reverts to slower letter-by-letter parsing. The gain you get from reduced crowding is wiped out by the loss of word-shape recognition.
3. Word spacing
The horizontal space between words. Adding 0.10–0.20em to word spacing makes word boundaries clearer, which helps readers who tend to "run words together" mentally. It's the gentlest of the three knobs — it rarely makes things noticeably worse, but its benefit is also smaller than letter spacing or line height. Think of it as the polish, not the foundation.
See the difference
The same paragraph at four different spacing settings. Read each one through and notice where your eye gets stuck or skims comfortably:
Reading is a coordinated act of pattern recognition. Your eye lands somewhere near the middle of each word, your brain reconstructs the rest, and then you leap forward. When letters are crowded too closely, the reconstruction step takes longer, and the leaps shorten. That is the friction that spacing tweaks are trying to remove.
Reading is a coordinated act of pattern recognition. Your eye lands somewhere near the middle of each word, your brain reconstructs the rest, and then you leap forward. When letters are crowded too closely, the reconstruction step takes longer, and the leaps shorten. That is the friction that spacing tweaks are trying to remove.
Reading is a coordinated act of pattern recognition. Your eye lands somewhere near the middle of each word, your brain reconstructs the rest, and then you leap forward. When letters are crowded too closely, the reconstruction step takes longer, and the leaps shorten. That is the friction that spacing tweaks are trying to remove.
Reading is a coordinated act of pattern recognition. Your eye lands somewhere near the middle of each word, your brain reconstructs the rest, and then you leap forward. When letters are crowded too closely, the reconstruction step takes longer, and the leaps shorten. That is the friction that spacing tweaks are trying to remove.
Most readers find the third example the most comfortable. The fourth one — which is roughly what some "extreme accessibility" presets push you to — feels open at first glance but is actually slower to read because each word floats in isolation and the eye has to leap further between them.
What the research actually found
Letter spacing: the strongest finding
Zorzi and colleagues' 2012 study, published in PNAS, tested 54 Italian and 40 French dyslexic children. With letter spacing increased to roughly +0.2em (a fairly aggressive amount, though the typography of the test materials was different from typical web defaults), reading speed improved by about 20% and reading errors dropped by roughly half. The effect was specific to dyslexic readers — non-dyslexic controls saw no benefit. Several follow-up studies in Spanish, German, and English have replicated the directional finding, though the effect size varies.
The study's authors argue this is the best evidence yet that visual crowding is a core mechanism in developmental dyslexia, not just a downstream symptom. That's a stronger claim than most font-design papers make.
Line height: an old finding, well established
Increased leading has been recommended by accessibility guidelines (BDA, WCAG 2.1 success criterion 1.4.12) for years, and the experimental support is broad if not always blockbuster. The headline finding across most studies: line-height of 1.5 reduces fixation duration on the start-of-line word — i.e. your eye lands more confidently on the right line — without any cost to reading speed for non-dyslexic readers. There's no real downside to setting line-height to 1.5 on the whole web.
Word spacing: weakest of the three
Most studies that vary word spacing alone find a small positive effect for dyslexic readers and essentially no effect for typical readers. It's not a placebo — there is signal — but the magnitude is smaller than letter spacing or line height. Treat it as a fine-tune, not a foundation.
Recommended values, in one place
| Setting | Recommended range | Notes |
|---|---|---|
| Font size (body) | 16–18 px (or 1.0–1.125 rem) | Anything below 14 px makes spacing tweaks less effective. |
| Line height | 1.5–1.7 | Start at 1.5, push to 1.7 if your eye loses its place on long paragraphs. |
| Letter spacing | +0.05em to +0.12em | BDA recommends +0.07em. Past +0.15em, word shapes dissolve. |
| Word spacing | +0.10em to +0.20em | Optional but cheap. Set once, forget. |
| Line length | 60–75 characters | Not strictly spacing, but affects line tracking. Above 80 characters, leading needs to grow. |
| Paragraph spacing | 1.5× line height | Visible breaks between paragraphs reduce skim fatigue. |
How to apply this on any website
Browsers don't expose spacing controls in the regular settings. To override site styles you have three practical options.
Option 1 — A dyslexia extension (easiest)
An extension like LexiFont exposes line height, letter spacing and word spacing as sliders, applies them to every site, and remembers your preferences. The free tier covers the basics; Pro unlocks per-site overrides if you want different values for, say, news sites versus documentation. If you've already read our piece on how to change the font on any website in Chrome, this is the same toolkit, just with the spacing knobs exposed.
Option 2 — Reader mode
Most browsers' built-in reader mode (Safari, Firefox, Edge) lets you bump line height and font size, though letter spacing usually isn't exposed. Reader mode also strips formatting, which is great for articles and useless for documentation, code, or anything tabular.
Option 3 — A user stylesheet
If you're comfortable with CSS, an extension like Stylus lets you write rules that apply to every page. A starter rule that matches the BDA recommendations:
p, li, td, th, blockquote {
line-height: 1.5 !important;
letter-spacing: 0.07em !important;
word-spacing: 0.16em !important;
}The !important flags are necessary because most sites set these properties themselves. The rule deliberately excludes headings (which have their own typographic logic) and code blocks (where letter spacing can break alignment).
Things that don't work as well as advertised
Justified text. Justification creates uneven word spacing across a line, which is the opposite of what you want. Always read in left-aligned (ragged-right) mode. The BDA explicitly recommends against full justification for dyslexic readers, and the evidence is solid.
Maximum-spacing presets. Some accessibility apps default to line-height of 2.0 and letter spacing of 0.2em on the theory that more is better. As the demo above shows, this is genuinely worse than 1.5/0.07. The "more spacing helps dyslexia" finding has a ceiling, and it's lower than people assume.
Centered body text. Centering each line forces your eye to find a different starting point for every row, which compounds line-tracking problems. Reserve it for headings and pull-quotes.
All-caps text. Capitals are roughly the same height, which removes the ascender/descender silhouette that helps the brain recognise words. Spacing tweaks can't compensate.
Combining spacing with the right font
Spacing and font choice multiply, they don't substitute for each other. The most comfortable combination for most dyslexic readers is a clean sans-serif with generous default spacing — Lexend or Atkinson Hyperlegible are good starting points — set at 1.5 line-height with +0.07em tracking. OpenDyslexic already builds in slightly looser spacing, so if you're using it you can drop letter spacing back toward zero.
Comic Sans, often discussed as a dyslexia-friendly default, has unusually generous letter spacing built in. That's part of why it works for some readers — and part of the reason Comic Neue is a slightly better choice: similar spacing characteristics, more polished letterforms.
A quick personal calibration
If you'd rather find your own values than trust the table above, here's a five-minute test:
Open a long article you've never read. Set line-height to 1.4, letter-spacing to 0, word-spacing to 0. Read for one minute and note how it feels. Bump line-height to 1.5; read another minute. Then 1.6, then 1.7. Whichever felt most comfortable is your line-height. Then repeat the same procedure for letter spacing in 0.03em increments from 0 to 0.12em. Don't tune both at once — you can't isolate which change helped.
Most readers land within one or two clicks of the BDA defaults. That's a reasonable confirmation that the consensus values are about right.