The text-rendering CSS property provides information to the rendering engine about what to optimize for when rendering text.

The browser makes trade-offs among speed, legibility, and geometric precision.

/* Keyword values */
text-rendering: auto;
text-rendering: optimizeSpeed;
text-rendering: optimizeLegibility;
text-rendering: geometricPrecision;

/* Global values */
text-rendering: inherit;
text-rendering: initial;
text-rendering: unset;

The text-rendering property is an SVG property that is not defined in any CSS standard. However, Gecko and WebKit browsers let you apply this property to HTML and XML content on Windows, Mac OS X and Linux.

One very visible effect is optimizeLegibility, which enables ligatures (ff, fi, fl, etc.) in text smaller than 20px for some fonts (for example, Microsoft's Calibri, Candara, Constantia, and Corbel, or the DejaVu font family).

Initial valueauto
Applies totext elements
Inheritedyes
Mediavisual
Computed valueas specified
Animation typediscrete
Canonical orderthe unique non-ambiguous order defined by the formal grammar

Syntax

Values

auto
The browser makes educated guesses about when to optimize for speed, legibility, and geometric precision while drawing text. For differences in how this value is interpreted by the browser, see the compatibility table.
optimizeSpeed
The browser emphasizes rendering speed over legibility and geometric precision when drawing text. It disables kerning and ligatures.
optimizeLegibility
The browser emphasizes legibility over rendering speed and geometric precision. This enables kerning and optional ligatures.
geometricPrecision

The browser emphasizes geometric precision over rendering speed and legibility. Certain aspects of fonts — such as kerning — don't scale linearly. So this value can make text using those fonts look good.

In SVG, when text is scaled up or down, browsers calculate the final size of the text (which is determined by the specified font size and the applied scale) and request a font of that computed size from the platform's font system. But if you request a font size of, say, 9 with a scale of 140%, the resulting font size of 12.6 doesn't explicitly exist in the font system, so the browser rounds the font size to 12 instead. This results in stair-step scaling of text.

But the geometricPrecision property — when fully supported by the rendering engine — lets you scale your text fluidly. For large scale factors, you might see less-than-beautiful text rendering, but the size is what you would expect—neither rounded up nor down to the nearest font size supported by Windows or Linux.

Note: WebKit precisely applies the specified value, but Gecko treats the value the same as optimizeLegibility.

Formal syntax

auto | optimizeSpeed | optimizeLegibility | geometricPrecision

Examples

optimizeLegibility automatically at 20px

<p class="small">LYoWAT - ff fi fl ffl</p>
<p class="big">LYoWAT - ff fi fl ffl</p>

This demonstates how optimizeLegibility is used by browsers automatically when the font-size is smaller than 20px:

.small { font: 19.9px 'DejaVu Serif', Constantia; }
.big   { font: 20px 'DejaVu Serif', Constantia; }

optimizeSpeed vs optimizeLegibility

<p class="speed">LYoWAT - ff fi fl ffl</p>
<p class="legibility">LYoWAT - ff fi fl ffl</p> 
p { font: 1.5em 'DejaVu Serif', Constantia; }

.speed       { text-rendering: optimizeSpeed; }
.legibility  { text-rendering: optimizeLegibility; }

Specifications

Specification Status Comment
Scalable Vector Graphics (SVG) 2
The definition of 'text-rendering' in that specification.
Candidate Recommendation No change
Scalable Vector Graphics (SVG) 1.1 (Second Edition)
The definition of 'text-rendering' in that specification.
Recommendation Initial definition

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support42 3 ?32 4 No155
auto Yes5 ? Yes6 No ? Yes7
geometricPrecision138 ? Yes9 No ? ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support31 ? ?46 No364.3
auto ? ? ? ? No ? ?
geometricPrecision ? ? ? ? No ? ?

1. From version 3 to 4.3, there is a serious bug where text-rendering: optimizeLegibility causes custom web fonts to not render. This was fixed in version 4.4.

2. This property is only supported on Windows and Linux.

3. Initial versions had bugs on Windows and Linux that broke font substitition, small-caps, letter-spacing or caused text to overlap.

4. The optimizeSpeed option has no effect on Firefox 4 because the standard code for text rendering is already fast and there is not a faster code path at this time. See bug 595688 for details.

5. Chrome treats auto as optimizeSpeed.

6. If the font size is 20 pixels or higher, Firefox treats auto as optimizeLegibility. For smaller text, Firefox treats auto as optimizeSpeed. The 20-pixel threshold can be changed with the browser.display.auto_quality_min_font_size preference.

7. Safari treats auto as optimizeSpeed. See WebKit bug 41363.

8. Supports true geometric precision without rounding up or down to the nearest supported font size in the operating system.

9. Firefox treats geometricPrecision the same as optimizeLegibility.

Document Tags and Contributors

 Last updated by: Sebastianz,