Blog · Typography
Line spacing and letter spacing for dyslexia — what actually matters
Most dyslexia font guides spend all their time on typeface choice and almost none on spacing. That is backwards. For many readers, adjusting the space between letters and between lines has a bigger effect than switching from Arial to OpenDyslexic. Here is what the research says, what numbers to aim for, and how to apply them without touching a stylesheet.
Two kinds of spacing — and why they matter differently
Before getting into the evidence it helps to be precise about terms, because "spacing" covers at least four distinct CSS properties and everyday conversation collapses all of them together.
Line spacing (called line-height in CSS, or leading in print) is the vertical distance from one baseline to the next. A line-height of 1.5 on 16px text gives 24px from one line's baseline to the next. Tight body text on most news sites runs around 1.3–1.4; generous editorial layouts run 1.6–1.8.
Letter spacing (called letter-spacing in CSS, or tracking in print) is the uniform space added or removed between every character in a run of text. It is different from kerning, which is the specific optical adjustment between pairs of letters — the gap between "AV" versus "MM" — and which is baked into the font itself. When dyslexia guides talk about letter spacing, they mean tracking: a flat offset applied to every character equally.
Word spacing (word-spacing in CSS) is the space between whole words. We have a dedicated article on word spacing and dyslexia — this article focuses on the other two dimensions.
What the evidence says about line spacing
The evidence here is more consistent than for almost any other typographic intervention studied in dyslexia research. Several independent groups have found that increased line spacing reduces reading errors in dyslexic readers, even when letter spacing and font are held constant.
The most-cited work is a 2012 study by Zorzi and colleagues, published in PNAS, that tested Italian primary-school children with dyslexia. The team found that simply increasing character and line spacing — without changing the font — reduced decoding errors by a significant margin and improved reading speed. The effect was specific to the dyslexic group; typical readers showed no improvement, which suggests the benefit is not a generic legibility gain but something specifically relevant to the dyslexic reading process.
The proposed explanation connects to what is known about crowding: the phenomenon where a target letter is harder to identify when flanking letters are close by. Dyslexic readers appear to have an unusually large crowding window — the zone around a letter that interferes with its recognition. Increasing line spacing reduces vertical crowding: the letters on the line above and below are farther away and create less interference. Increasing letter spacing reduces horizontal crowding in the same way.
A 2016 review by Rello and Bigham collected a wider range of typographic studies and reached similar conclusions. Line height between 1.5 and 1.8 times the font size consistently outperformed tighter settings in reading accuracy tests with dyslexic participants. The sweet spot in most studies was around 1.5–1.6 — wide enough to reduce crowding without creating so much vertical separation that the eye loses track of which line it is on.
Practical target: aim for a line-height of at least 1.5 times the font size. If the page you are reading has tight 1.2 or 1.3 line spacing — common on news sites and academic journals — the visual crowding this creates may be a larger source of reading difficulty than the font itself.
What the evidence says about letter spacing
Letter spacing research is slightly messier than line spacing research, partly because different fonts have different default spacing built in, and partly because the optimal tracking depends on the font's x-height and stroke contrast. The directionality is clear, though: for dyslexic readers, slightly more letter spacing is almost always better than less — up to a point.
The Zorzi 2012 study used an extra-large letter spacing (roughly 2.5 times the standard spacing for the font tested) and found clear benefits. More recent work has looked at more moderate increases and found that even modest additions — on the order of 0.05–0.12em — improve accuracy without the text feeling artificially spread out.
The British Dyslexia Association's style guide recommends a minimum of 35 thousandths of an em (0.035em) of additional letter spacing for dyslexia-accessible body text. The W3C's WCAG 2.1 Success Criterion 1.4.12 — the "text spacing" criterion — specifies that content must not lose information or functionality when letter spacing is set to at least 0.12em above the font's default. That is the floor for web accessibility compliance, not a recommendation for dyslexia specifically, but it gives a useful lower bound.
One finding that surprises people: OpenDyslexic, arguably the most recognisable dyslexia font, already has generous letter spacing baked in. Part of what makes it feel different from Arial or Times New Roman is not just the weighted-bottom letterforms — it is that the default tracking is wider. If you switch from a tight font to OpenDyslexic and feel immediate relief, some of what you are responding to may be the spacing, not the shapes. See our guide to the best fonts for dyslexia in 2026 for a full breakdown of how different typefaces approach spacing by default.
Seeing the difference
Here is the same paragraph rendered at three different line-height and letter-spacing combinations. The content is identical — only the spacing changes.
The crowding effect means that letters surrounded by other letters are harder to recognise than isolated letters. For dyslexic readers, the crowding window is wider than average, so interference extends further across the line — both horizontally into adjacent letters and vertically from the lines above and below.
The crowding effect means that letters surrounded by other letters are harder to recognise than isolated letters. For dyslexic readers, the crowding window is wider than average, so interference extends further across the line — both horizontally into adjacent letters and vertically from the lines above and below.
The crowding effect means that letters surrounded by other letters are harder to recognise than isolated letters. For dyslexic readers, the crowding window is wider than average, so interference extends further across the line — both horizontally into adjacent letters and vertically from the lines above and below.
Read all three and notice where your eye moves most easily. The tight version is not merely harder on a slow reading day — for readers with dyslexia, it imposes a measurable cognitive cost on every word.
Recommended values
Based on published research and the BDA and WCAG guidelines, here are the ranges worth aiming for in body text:
| Property | Too tight | Good range | Upper limit |
|---|---|---|---|
| Line height | Below 1.4 | 1.5–1.8 | Around 2.0 (line-tracking becomes hard) |
| Letter spacing | Negative or zero on condensed fonts | 0.03em–0.12em above font default | 0.15em (words feel disjointed) |
| Word spacing | Below 1.16 times normal | 1.16–1.4 times normal | 1.5 times (words read as isolated units) |
These are starting points, not prescriptions. Reading is individual, and the right values depend on your font, screen size, and particular reading pattern. The goal is the widest spacing that still feels like continuous prose — not a list of separated fragments.
The WCAG 1.4.12 text-spacing rule
Web Content Accessibility Guidelines criterion 1.4.12 requires that no content be lost or obscured when a user sets letter spacing to 0.12em above the default, word spacing to 0.16em, line height to 1.5 times the font size, and paragraph spacing to 2 times the font size. Sites that pass this criterion will not break their layout when a browser extension overrides their CSS — meaning you can apply these settings globally without pages falling apart.
In practice, many sites still fail 1.4.12. Navigation menus collapse, hero text overflows its container, and sidebars push into the main column. If you use a font-override tool like LexiFont and notice overlapping text or broken navigation, that is usually the site failing its accessibility obligations rather than a problem with the extension. It is also non-compliant with accessibility law in the EU, UK, and several US regulatory frameworks that reference WCAG as a standard.
How to apply spacing changes in Chrome without touching CSS yourself
Reader mode. Chrome's built-in reader mode (the icon in the address bar on long articles) reformats pages with its own font and wider margins. It does not give you control over letter spacing, but it is a one-click improvement on most news sites. For more on this, see our comparison of strategies for reading long articles with dyslexia.
Font-override extensions. LexiFont overrides the typeface on every page, and LexiFont Pro adds global control over letter spacing and line height as CSS variables applied sitewide. This is the approach that gives you consistent spacing across all sites without configuring each one manually.
Custom stylesheets. If you are comfortable with developer tools, you can inject a user stylesheet via an extension like Stylus. The relevant CSS is simple:
body, p, li, td, th {
line-height: 1.6 !important;
letter-spacing: 0.05em !important;
word-spacing: 0.1em !important;
}
The !important declaration is necessary to override site styles. Accept that it may break poorly coded layouts on some sites.
Zoom. Browser zoom (Ctrl/Cmd +) increases font size but does not change line-height ratios or letter-spacing values — it scales everything proportionally. Zoom helps with small text but does not fix tight spacing.
When spacing matters more than font choice
The dyslexia reading community spends considerable energy debating OpenDyslexic vs Lexend vs Atkinson Hyperlegible — and those differences are real. But the research suggests spacing is often the stronger variable, particularly for readers whose main difficulty is crowding rather than letter-shape confusion.
If you have tried multiple dyslexia fonts and found the gains modest, try a spacing adjustment before concluding that fonts cannot help you. A tight sans-serif at 1.6 line height may read more comfortably than OpenDyslexic at 1.2 line height. Conversely, if you have already adjusted spacing and are still struggling, that is the moment to experiment with letter shapes — the serif vs sans-serif research for dyslexic readers and our breakdown of font weight and dyslexia may be useful here.
Reading difficulty in dyslexia is not one thing with one fix. Crowding, letter-shape confusion, tracking difficulty, and working memory load all contribute, and they do not all respond to the same intervention. Spacing targets crowding directly. Font choice targets letter-shape confusion. They work on different parts of the problem and stack rather than substitute.
For a fuller picture of how the components of reading difficulty interact, see our article on why dyslexic readers lose their place on the page — which covers the role of saccades and fixation points — and our piece on working memory and adult dyslexia.
Quick test: find an article on a news site with tight spacing. Copy one paragraph into a plain text editor, set the font to something simple at size 16, and adjust the line height to 1.7. If reading feels noticeably easier, spacing is a significant variable for you and worth adding to your browser setup permanently.