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;
aspect-ratio: 1;

/* Global values */
aspect-ratio: inherit;
aspect-ratio: initial;
aspect-ratio: revert;
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. If height and the preceding slash character are omitted, height defaults to 1. 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;
aspect-ratio: 0.5;

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
CSS Box Sizing Module Level 4 (CSS Sizing 4) # aspect-ratio

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`aspect-ratio`	88 84	88	89 83 Firefox 83 implements aspect-ratio for flex items. 81 Firefox 81 implements aspect-ratio for blocks and replaced elements.	No	74	15	88	88	89	63	15	15.0