font-optical-sizing CSS property

The font-optical-sizing CSS property sets whether text rendering is optimized for viewing at different sizes.

Try it

font-optical-sizing: auto;
font-optical-sizing: none;
<section id="default-example">
  <div id="example-element">
    <h2>Chapter 3</h2>
    <p>
      On this particular Thursday, something was moving quietly through the
      ionosphere many miles above the surface of the planet; several somethings
      in fact, several dozen huge yellow chunky slablike somethings, huge as
      office blocks, silent as birds.
    </p>
  </div>
</section>
@font-face {
  src: url("/shared-assets/fonts/variable-fonts/AmstelvarAlpha-VF.ttf");
  font-family: "Amstelvar";
  font-style: normal;
}

#example-element {
  font-family: "Amstelvar", serif;
  text-align: left;
}

#example-element h2 {
  font-size: 36px;
}

#example-element p {
  font-size: 12px;
}

Syntax

css
/* keyword values */
font-optical-sizing: none;
font-optical-sizing: auto; /* default */

/* Global values */
font-optical-sizing: inherit;
font-optical-sizing: initial;
font-optical-sizing: revert;
font-optical-sizing: revert-layer;
font-optical-sizing: unset;

Values

This property is specified as one of the following keyword values:

none

The browser will not modify the shape of glyphs for optimal viewing.

auto

The browser will modify the shape of glyphs for optimal viewing.

Description

Optical sizing is enabled by default for fonts that have an optical size variation axis. The optical size variation axis is represented by opsz in font-variation-settings.

When optical sizing is used, small text sizes are often rendered with thicker strokes and larger serifs, whereas larger text is often rendered more delicately with more contrast between thicker and thinner strokes.

Formal definition

Initial valueauto
Applies toall elements and text. It also applies to ::first-letter and ::first-line.
Inheritedyes
Computed valueas specified
Animation typediscrete

Formal syntax

font-optical-sizing = 
  auto  |
  none

Examples

undefined

Disabling optical sizing

html
<p class="optical-sizing">
  This paragraph is optically sized. This is the default across browsers.
</p>

<p class="no-optical-sizing">
  This paragraph is not optically sized. You should see a difference in
  supporting browsers.
</p>
css
@font-face {
  src: url("AmstelvarAlpha-VF.ttf");
  font-family: "Amstelvar";
  font-style: normal;
}

p {
  font-size: 36px;
  font-family: "Amstelvar", serif;
}

.no-optical-sizing {
  font-optical-sizing: none;
}

Note: The font referenced above — which includes optical sizing and is freely-licensed — is good for testing. You can download it on GitHub.

Specifications

See also