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

Try it


/* 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;



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


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


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. It also applies to ::first-letter and ::first-line.
Computed valueas specified
Animation typediscrete

Formal syntax

font-optical-sizing = 
auto |


Disabling optical sizing

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

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


CSS Fonts Module Level 4
# font-optical-sizing-def

Browser compatibility

BCD tables only load in the browser

See also