HTMLImageElement: sizes property

The HTMLImageElement property sizes allows you to specify the layout width of the image for each of a list of media conditions. This provides the ability to automatically select among different images—even images of different orientations or aspect ratios—as the document state changes to match different media conditions.

Each condition is specified using the same conditional format used by media queries.


A string containing a comma-separated list of source size descriptors followed by an optional fallback size. Each source size descriptor is comprised of a media condition, then at least one whitespace character, then the source size value to use for the image when the media condition evaluates to true.

Media conditions

Each source size descriptor consists of a media condition as defined by the media queries standard. Because a source size descriptor is used to specify the width to use for the image during layout of the page, the media condition is typically (but not necessarily) based entirely on width information. See Using media queries, Syntax for details on how to construct a media condition.

Source size values

The source size value is a CSS <length>. It may be specified using font-relative units (such as em or ex), absolute units (such as px or cm), or the vw unit, which lets you specify the width as a percentage of the viewport width (1vw being 1% of the viewport width).

Note: The source size value must not be specified as a percentage of the container size; that is, lengths such as 50% or 100% are not allowed, as there would be uncertainty as to what the specified value is a percentage of.


Selecting an image to fit window width

In this example, a blog-like layout is created, displaying some text and an image for which three size points are specified, depending on the width of the window. Three versions of the image are also available, with their widths specified. The browser takes all of this information and selects an image and width that best meets the specified values.

How exactly the images are used may depend upon the browser and the pixel density of the user's display.

Buttons at the bottom of the example let you actually modify the sizes property slightly, switching the largest of the three widths for the image between 40em and 50em.


  <h1>An amazing headline</h1>
  <div class="test"></div>
    This is even more amazing content text. It's really spectacular. And
    fascinating. Oh, it's also clever and witty. Award-winning stuff, I'm sure.
      new-york-skyline-wide.jpg 3724w,
      new-york-skyline-4by3.jpg 1961w,
      new-york-skyline-tall.jpg 1060w
    sizes="((min-width: 50em) and (max-width: 60em)) 50em,
              ((min-width: 30em) and (max-width: 50em)) 30em,
              (max-width: 30em) 20em"
    alt="The New York City skyline on a beautiful day, with the One World Trade Center building in the middle." />
    Then there's even more amazing stuff to say down here. Can you believe it? I
    sure can't.

  <button id="break40">Last Width: 40em</button>
  <button id="break50">Last Width: 50em</button>


article {
  margin: 1em;
  max-width: 60em;
  min-width: 20em;
  border: 4em solid #880e4f;
  border-radius: 7em;
  padding: 1.5em;
    16px "Open Sans",

article img {
  display: block;
  max-width: 100%;
  border: 1px solid #888;
  box-shadow: 0 0.5em 0.3em #888;
  margin-bottom: 1.25em;


The JavaScript code handles the two buttons that let you toggle the third width option between 40em and 50em; this is done by handling the click event, using the JavaScript string replace() method to replace the relevant portion of the sizes string.

const image = document.querySelector("article img");
const break40 = document.getElementById("break40");
const break50 = document.getElementById("break50");

  () => (image.sizes = image.sizes.replace(/50em,/, "40em,")),

  () => (image.sizes = image.sizes.replace(/40em,/, "50em,")),


The page is best viewed in its own window, so you can adjust the sizes fully.


HTML Standard
# dom-img-sizes

Browser compatibility

BCD tables only load in the browser

See also