The HTTP Sec-CH-DPR request header provides device client hints about the client device pixel ratio (DPR). This ratio is the number of physical device pixels corresponding to every CSS pixel.

The hint is useful when selecting image sources that best correspond to a screen's pixel density. This is similar to the role played by x descriptors in the <img> srcset attribute to allow user agents to select a preferred image.

If the Sec-CH-DPR header appears more than once in a message the last occurrence is used.

Servers that opt in to the Sec-CH-DPR client hint will typically also specify it in the Vary header to inform caches that the server may send different responses based on the header value in a request.

Syntax

Sec-CH-DPR: <number>

Directives

<number>

The client device pixel ratio.

Examples

A server must first opt in to receive the Sec-CH-DPR header by sending the response header Accept-CH containing the directive Sec-CH-DPR.

Accept-CH: Sec-CH-DPR

Then on subsequent requests the client might send Sec-CH-DPR header to the server:

Sec-CH-DPR: 2.0

Specifications

Browser compatibility

See also

• Device and responsive image client hints
  • Sec-CH-Device-Memory
  • Sec-CH-Viewport-Height
  • Sec-CH-Viewport-Width
  • DPR
• Accept-CH
• HTTP Caching: Vary and Vary
• Improving user privacy and developer experience with User-Agent Client Hints (developer.chrome.com)