text-rendering property CSS Reference



Definition and Usage

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. 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 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 auto
  • Applies to text elements
  • Inherited yes
  • Media visual
  • Computed Value NA

Syntax

Formal grammar:  auto | optimizeSpeed | optimizeLegibility | geometricPrecision
text-rendering: auto
text-rendering: optimizeSpeed
text-rendering: optimizeLegibility
text-rendering: geometricPrecision
text-rendering: inherit

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 geometricPrecision 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 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.

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


Examples

/* make sure all fonts in the HTML document display in all its glory,
but avoid inadequate ligatures in class foo elements */
body  { text-rendering: optimizeLegibility; }
.foo  { text-rendering: optimizeSpeed; }
Live Example
CSS code Kerning Ligatures
font: 19.9px 'DejaVu Serif',Constantia; LYoWAT ff fi fl ffl
font: 20px 'DejaVu Serif',Constantia; LYoWAT ff fi fl ffl
font: 3em 'DejaVu Serif',Constantia; text-rendering: optimizeSpeed; LYoWAT ff fi fl ffl
font: 3em 'Dejavu Serif',Constantia; text-rendering: optimizeLegibility; LYoWAT ff fi fl ffl

Compatibility

Desktop browsers

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support for Windows and Linux

4.0 but the implementation known bugs on Windows and Linux which can break font substitition, small-caps, letter-spacing or cause text to overlap

3.0 (1.9) Not supported Not supported 5.0 (532.5)
Basic support for other operating systems Not supported Not supported Not supported Not supported Not supported
auto Chrome treats this as optimizeSpeed.
Work is continuing on (WebKit bug 41363)
If the font size is 20 px or higher, Gecko browsers use optimizeLegibility; for smaller text, they use optimizeSpeed. Not supported Not supported Safari treats this as optimizeSpeed.
Work is continuing on (WebKit bug 41363)
geometricPrecision 13 supports true geometric precision, without rounding up or down to the nearest supported font size in the operating system.
Introduced in WebKit 535.1 (WebKit bug 60317)
Gecko treats the value the same as optimizeLegibility. Not supported Not supported  

Mobile browsers

Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support NA NA NA NA NA

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