The font-optical-sizing CSS property allows developers to control whether browsers render text with slightly differing visual representations to optimize viewing at different sizes, or not. This only works for fonts that have an optical size variation axis.

For example, 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.

Note: The optical size variation axis is represented by opsz in font-variation-settings.


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

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


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

Formal syntax

auto | none


<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>
@font-face {
    src: url('AmstelvarAlpha-VF.ttf');
    font-style: normal;

p {
  font-size: 36px;
  font-family: Amstelvar;

.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.


Specification Status Comment
CSS Fonts Module Level 4
The definition of 'font-optical-sizing' in that specification.
Working Draft  

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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support ? ?


60 — 621

No ? ?
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support ? ? ?


60 — 621

? ? ?

1. From version 60 until version 62 (exclusive): this feature is behind the layout.css.font-variations.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.

Document Tags and Contributors

Contributors to this page: chrisdavidmills
Last updated by: chrisdavidmills,