HTML <source> sizes Attribute

The sizes attribute on a <source> element specifies the width for an image depending on browser dimensions. This attribute helps create responsive images that vary depending on browser conditions.

Example

#

A sizes attribute on a <source> element.
Resizing the browser will adjust the image file that will display.

Vincent Van Gogh
<picture>
  <source srcset="/img/html/vangogh-sm.jpg 120w,
                  /img/html/vangogh.jpg 193w,
                  /img/html/vangogh-lg.jpg 278w"
          sizes="(max-width: 710px) 120px,
                 (max-width: 991px) 193px,
                 278px">
  
  <img src="/img/html/vangogh-lg.jpg" alt="Vincent Van Gogh">
</picture>


The three images of different size.

Code Explanation

A small image is used with a screen between 0 - 710px. The layout width is 120px.

A medium image is used with a screen between 711px - 991px. The layout width is 193px.

A large image is used with a screen 992px and larger. The layout width is 278px.

See below for a detailed description.


Using sizes

The srcset attribute specifies multiple image URLs and image sizes.

Together with the sizes attribute they create responsive images that adjust according to browser conditions.

Each size in the sizes attribute has the following format: (media-condition) width

  • media-condition = Media query (e.g max-width: 540px), followed by a space.
  • width = The width of the available space in pixels (px), em, or viewport (vw).
  • Multiple sizes are comma-separated. Here is an example:
<source srcset="/img/new-york-sm.jpg 120w,
                /img/new-york-md.jpg 200w,
                /img/new-york-lg.jpg 300w"
        sizes="((min-width: 10em) and (max-width: 20em)) 10em,
               ((min-width: 30em) and (max-width: 40em)) 30em,
                (min-width: 40em) 40em">

Syntax

<source sizes="(media-condition) width">

Note: Multiple values are comma-separated.


Values

#

Value Description
(media-condition) width A media-query followed by the image layout width.
The layout width can be defined with px, em, or vw.

Browser support

Here is when sizes support started for each browser:

Chrome
34.0 Apr 2014
Firefox
38.0 May 2015
IE/Edge
16.0 Oct 2017
Opera
25.0 Oct 2014
Safari
9.0 Sept 2015

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