The sizes attribute on an <source> element specifies different image widths.
These widths are tied to browser conditions which helps create responsive images.
A sizes attribute on a <source> element.
Resizing the browser will adjust the image file that will display.
<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.
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.
The srcset and sizes attributes work together to create responsive images.
The srcset attribute points to image URLs.
And sizes specifies image sizes and browser conditions (media queries).
Each size in sizes 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).<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">
<source sizes="(media-condition) width">
Note: Multiple values are comma-separated.
| 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. |
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 |
