The blur() CSS function applies a Gaussian blur to the input image. Its result is a <filter-function>.

Try it

filter: blur(0);

filter: blur(4px);

filter: blur(1.5rem);

<section id="default-example">
  <img
    class="transition-all"
    id="example-element"
    src="/shared-assets/images/examples/firefox-logo.svg"
    width="200" />
</section>

Syntax

blur(radius)

Parameters

radius Optional

The radius of the blur, specified as a <length>. It defines the value of the standard deviation to the Gaussian function, i.e., how many pixels on the screen blend into each other; thus, a larger value will create more blur. A value of 0 leaves the input unchanged. The initial value for interpolation is 0. Percentage values are invalid. The default value is 0px.

Examples of blur values

blur()         /* No effect */
blur(0)        /* No effect */

blur(8px)      /* Blur with 8px radius */
blur(1.17rem)  /* Blur with 1.17rem radius */

SVG filter

The SVG <feGaussianBlur> filter element can also be used to blur content. The filter's stdDeviation attribute accepts up to two values enabling creating more complex blur values. To create an equivalent blur, we include one value for stdDeviation. This SVG effect can then be referenced by ID:

<svg role="none">
  <filter id="blur11">
    <feGaussianBlur stdDeviation="1.1" edgeMode="duplicate" />
  </filter>
</svg>

The following declarations produce the same effect:

filter: blur(1.1px);
filter: url("#blur11"); /* with embedded SVG */
filter: url("folder/fileName.svg#blur11"); /* external svg filter definition */

Formal syntax

<blur()> = 
  blur( <length>? )  

Examples

This example shows three images: the image with a blur() filter function applied, the image with the equivalent SVG blur function applied, and the original images for comparison:

.filter {
  filter: blur(3.5px);
}

<svg role="img" aria-label="Flag">
  <filter id="blur">
    <feGaussianBlur stdDeviation="3.5" edgeMode="duplicate" />
  </filter>
  <image
    href="https://mdn.github.io/shared-assets/images/examples/progress-pride-flag.jpg"
    xlink:href="https://mdn.github.io/shared-assets/images/examples/progress-pride-flag.jpg"
    filter="url('#blur')" />
</svg>

Specifications

Browser compatibility

See also

• CSS filter effects module
• The other <filter-function> functions available to be used in values of the filter and backdrop-filter properties include:
  • brightness()
  • contrast()
  • drop-shadow()
  • grayscale()
  • hue-rotate()
  • invert()
  • opacity()
  • saturate()
  • sepia()