`blur()` CSS function

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

css

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

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

Parameters

<length> Optional: Specifies the radius of the blur. It defines the value of the standard deviation to the Gaussian function, that is, how many pixels on the screen blend into each other. Therefore, 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 0.

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:

html

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

The following declarations produce the same effect:

css

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:

css

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