Techniques for WCAG 2.0

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G178: Providing controls on the Web page that allow users to incrementally change the size of all text on the page up to 200 percent


All technologies.

This technique relates to:


The purpose of this technique is to provide a mechanism on the Web page to incrementally increase the size of text. Many people with low vision do not use magnifying software, and they may not be familiar with browsers text size adjustments. This may be particularly true of older people who are learning about computers later in life and who may be experiencing age related vision loss. It may also be true of some people with cognitive disabilities who also require increased font size.

This technique provides a mechanism that some users will find easier to use. The mechanism may include links or buttons that will switch the visual presentation to a different style sheet or use scripts to change the text size dynamically.

To implement this technique, an author provides controls that allow the user to incrementally increase or decrease the text size of all of the text on the page to a size that is at least 200% of the default text size.

This can be achieved by providing links, buttons or linked images and the controls themselves should be as easy to find (ex. prominently positioned within the page, presented in a larger text size, hight contrast, etc.) as possible.

This technique can also be used in circumstances where scalable fonts cannot be used, such as legacy code situtions.

Note: This technique can be used in combination with a style switching technique to present a page that is a conforming alternate version for non-conforming content. Refer to C29: Using a style switcher to provide a conforming alternate version (CSS) and Understanding Conforming Alternate Versions for more information.




  1. Set the viewport size to 1024px by 768px or larger.

  2. Increase the text size and check to see if the text size increased.

  3. Check that the text size can be increased to 200% of the original size.

  4. Check that after increasing the text size to 200% of the original size, there is no loss of content or functionality (e.g. no parts of the text are clipped, boxes do not overlap, controls are not obscured or separated from their labels, etc.).

  5. Decrease the text size to its default value and check to see if it in fact returned to the default size.

Expected Results

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.

Techniques are Informative

Techniques are informative—that means they are not required. The basis for determining conformance to WCAG 2.0 is the success criteria from the WCAG 2.0 standard—not the techniques. For important information about techniques, please see the Understanding Techniques for WCAG Success Criteria section of Understanding WCAG 2.0.