Width Header

Table of Content

The Width header is an integral part of web technologies, particularly in the development and design of layouts for websites and web applications. This header plays a pivotal role in specifying the width of various elements such as images, tables, div elements, etc., in CSS (Cascading Style Sheets). Understanding and utilizing this header can be pivotal in creating aesthetically pleasing and responsive designs.


width: <value> | <percentage> | auto


There are three directives associated with the Width header.

  • <value>: Specifies the width in a unit measurement such as px (pixels), em, rem, etc.
  • <percentage>: Defines the width as a percentage of the parent element's width.
  • auto: The width is automatically set by the browser depending on content and available space.


Here are some examples of how to use the Width header:

  • Fixed width: width: 200px;
  • Percentage width: width: 50%;
  • Automatic width: width: auto;

Browser Compatibility

Browser Compatibility
Chrome Supported
Firefox Supported
Safari Supported
Opera Supported
Edge Supported

How to modify Width header

ModHeader is a Google Chrome extension that allows you to modify headers on HTTP(S) requests. You can use ModHeader to adjust the Width header in either your development or testing process.

Once ModHeader is installed, you can open it in your browser's toolbar, select 'Add profile', give it a name, and start adding headers. For the Width header, you'd input Width under 'Header name' and whatever width you desire (e.g. "100px", "50%", or "auto") under 'Header value'. This can be particularly useful when testing how a website or web application responds to different screen widths, without having to manually adjust the browser window or use a variety of devices for testing.