DPR
===

**Deprecated:** This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

**Secure context:** This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

**Non-standard:** This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The **`DPR`** device client hint request header provides the client device pixel ratio. This ratio is the number of physical device pixels corresponding to every CSS pixel.

|  |  |
| --- | --- |
| Header type | Request header,
 Client hint |
| Forbidden header name | no |

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 a server uses the `DPR` hint to choose which resource is sent in a response, the response must include the `Content-DPR` header. The client must use the value in `Content-DPR` for layout if it differs from the value in the request's `DPR` header.

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

**Note:**

* Client Hints are accessible only on secure origins (via TLS).
* A server has to opt in to receive the `DPR` header from the client, by sending the `Accept-CH` response header.
* Servers that opt in to the `DPR` client hint will typically also specify it in the `Vary` header. This informs caches that the server may send different responses based on the header value in a request.
* `DPR` was removed from the client hints specification in draft-ietf-httpbis-client-hints-07. The proposed replacement is `Sec-CH-DPR` (Responsive Image Client Hints).

Syntax
------


```http
DPR: <number>
```

Directives
----------

`<number>`

The client device pixel ratio.

Examples
--------

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


```http
Accept-CH: DPR
```


Then on subsequent requests the client might send `DPR` header to the server:


```http
DPR: 2.0
```


If a request with the `DPR` header (as shown above) is for an image resource, then the server response must include the `Content-DPR` header:


```http
Content-DPR: 2.0
```

Browser compatibility
---------------------

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

See also
--------

* Improving user privacy and developer experience with User-Agent Client Hints (developer.chrome.com)
* Device client hints
    + `Content-DPR`
    + `Device-Memory`
    + `Viewport-Width`
    + `Width`
* `Accept-CH`
* HTTP Caching > Vary and `Vary`