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aspect-ratio

The aspect-ratio CSS property sets a preferred aspect ratio for the box, which will be used in the calculation of auto sizes and some other layout functions.

aspect-ratio: 1 / 1;

/* Global values */
aspect-ratio: inherit;
aspect-ratio: initial;
aspect-ratio: unset;

Values

<auto>: Replaced elements with an intrinsic aspect ratio use that aspect ratio, otherwise the box has no preferred aspect ratio. Size calculations involving intrinsic aspect ratio always work with the content box dimensions.
<ratio>: The box’s preferred aspect ratio is the specified ratio of width / height. Size calculations involving preferred aspect ratio work with the dimensions of the box specified by box-sizing.

Formal definition

Initial value	`auto`
Applies to	all elements except inline boxes and internal ruby or table boxes
Inherited	no
Computed value	as specified
Animation type	discrete

Formal syntax

auto | <ratio>

Examples

Examples of values for aspect-ratio

aspect-ratio: 1 / 1; 
aspect-ratio: 16 / 9;

Mapping width and height to aspect-ratio

Browsers have added an internal aspect-ratio property that applies to replaced elements and other related elements that accept width and height attributes. This appears in the browser's internal UA stylesheet.

In Firefox, the internal stylesheet rule looks like this:

img, input[type="image"], video, embed, iframe, marquee, object, table {
  aspect-ratio: attr(width) / attr(height);
}

You can read more about this feature in Setting Height And Width On Images Is Important Again.

Specifications

Specification	Status	Comment
CSS Box Sizing Module Level 4 The definition of 'aspect-ratio' in that specification.	Editor's Draft	Initial definition

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
`aspect-ratio`	79 79 Chrome 79 adds internal support only for mapped values	79 79 Edge 79 adds internal support only for mapped values	71 71 Firefox 71 adds internal support only for mapped values 69 — 71 Disabled Firefox 69 adds internal support only for mapped values Disabled From version 69 until version 71 (exclusive): this feature is behind the `layout.css.width-and-height-map-to-aspect-ratio.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No	No	14 14 Safari 14 adds internal support only for mapped values
Internal mapping of width and height	79	79	71 71 69 — 71 Disabled Disabled From version 69 until version 71 (exclusive): this feature is behind the `layout.css.width-and-height-map-to-aspect-ratio.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	No	No	14

	Mobile
	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`aspect-ratio`	79 79 Webview 79 adds internal support only for mapped values	79 79 Chrome 79 adds internal support only for mapped values	No	No	14 14 Safari 14 adds internal support only for mapped values	12.0 12.0 Samsung Internet 12.0 adds internal support only for mapped values
Internal mapping of width and height	79	79	No	No	14	12.0