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Content-Length header

files/en-us/web/http/reference/headers/content-length/index.md

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The HTTP Content-Length header indicates the size, in bytes, of the message body sent to the recipient.

Content-Length is limited in that the message size must be known up front, before sending the headers, which is a problem when content is dynamically generated or streamed.

  • In HTTP/1.0, it is required.
  • In HTTP/1.1, it could be replaced with {{httpheader("Transfer-Encoding", "Transfer-Encoding: chunked")}} for responses sent out in parts as its size is calculated.
  • In HTTP/2, Content-Length is redundant, because the content length may be inferred from DATA frames. It may still be included for backwards compatibility.
<table class="properties"> <tbody> <tr> <th scope="row">Header type</th> <td> {{Glossary("Request header")}}, {{Glossary("Response header")}}, {{Glossary("Content header")}} </td> </tr> <tr> <th scope="row">{{Glossary("Forbidden request header")}}</th> <td>Yes</td> </tr> <tr> <th scope="row"> {{Glossary("CORS-safelisted response header")}} </th> <td>Yes</td> </tr> </tbody> </table>

Syntax

http
Content-Length: <length>

Directives

  • <length>
    • : The length in octets.

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

  • {{HTTPHeader("Transfer-Encoding")}}