Understanding Success Criterion 1.4.4: Resize text

Except for captions and images of text, text can be resized without assistive technology up to 200 percent without loss of content or functionality.

Intent of Success Criterion 1.4.4: Resize text

The intent of this Success Criterion is to ensure that visually rendered text, including text-based controls (text characters that have been displayed so that they can be seen [vs. text characters that are still in data form such as ASCII]) can be scaled successfully so that it can be read directly by people with mild visual disabilities, without requiring the use of assistive technology such as a screen magnifier. Users may benefit from scaling all content on the Web page, but text is most critical.

The scaling of content is primarily a user agent responsibility. User agents that satisfy UAAG 1.0 Checkpoint 4.1 allow users to configure text scale. The author's responsibility is to create Web content that does not prevent the user agent from scaling the content effectively. Authors may satisfy this Success Criterion by verifying that content does not interfere with user agent support for resizing text, including text-based controls, or by providing direct support for resizing text or changing the layout. An example of direct support might be via server-side script that can be used to assign different style sheets.

The author cannot rely on the user agent to satisfy this Success Criterion for HTML content if users do not have access to a user agent with zoom support. For example, if they work in an environment that requires them to use IE 6.

If the author is using a technology whose user agents do not provide zoom support, the author is responsible to provide this type of functionality directly or to provide content that works with the type of functionality provided by the user agent. If the user agent doesn't provide zoom functionality but does let the the user change the text size, the author is responsible for ensuring that the content remains usable when the text is resized.

Some user interface components that function as a label and require activation by the user to access content are not wide enough to accommodate the label's content. For example, in Web mail applications the subject column may not be wide enough to accommodate every possible subject header, but activating the subject header takes the user to the full message with the full subject header. In Web-based spreadsheets, cell content that is too long to be displayed in a column can be truncated, and the full content of the cell is available to the user when the cell receives focus. The content of a user interface component may also become too wide in user interfaces where the user can resize the column width. In this type of user interface component, line wrapping is not required; truncation is acceptable if the component's full content is available on focus or after user activation and an indication that this information can be accessed, is provided to the user in some way besides the fact that it is truncated.

Content satisfies the Success Criterion if it can be scaled up to 200%, that is, up to twice the width and height. Authors may support scaling beyond that limit, however, as scaling becomes more extreme, adaptive layouts may introduce usability problems. For example, words may be too wide to fit into the horizontal space available to them, causing them to be truncated; layout constraints may cause text to overlap with other content when it is scaled larger; or only one word of a sentence may fit on each line, causing the sentence to be displayed as a vertical column of text that is difficult to read.

The working group feels that 200% is a reasonable accommodation that can support a wide range of designs and layouts, and complements older screen magnifiers that provide a minimum magnification of 200%. Above 200%, zoom (which resizes text, images, and layout regions and creates a larger canvas that may require both horizontal and vertical scrolling) may be more effective than text resizing. Assistive technology dedicated to zoom support would usually be used in such a situation and may provide better accessibility than attempts by the author to support the user directly.

Images of text do not scale as well as text because they tend to pixelate, and therefore we suggest using text wherever possible. It is also harder to change foreground and background contrast and color combinations for images of text, which are necessary for some users.

See also .

Benefits of Success Criterion 1.4.4: Resize text

  • This Success Criterion helps people with low vision by letting them increase text size in content so that they can read it.

Examples of Success Criterion 1.4.4: Resize text

  • A user with vision impairments increases the text size on a Web page in a browser from 1 em to 1.2 ems. While the user could not read the text at the smaller size, she can read the larger text. All the information on the page is still displayed when the larger font is used for the text.
  • A Web page contains a control for changing the scale of the page. Selecting different settings changes the layout of the page to use the best design for that scale.
  • A user uses a zoom function in his user agent to change the scale of the content. All the content scales uniformly, and the user agent provides scroll bars, if necessary.

Resources Success Criterion 1.4.4: Resize text

Techniques for Success Criterion 1.4.4: Resize text

Sufficient Techniques

  1. Using a technology that has commonly-available user agents that support zoom
  2. SL22
  3. SL23
  4. Ensuring that text containers resize when the text resizes AND using measurements that are relative to other measurements in the content by using one or more of the following techniques:

  5. Providing controls on the Web page that incrementally change the size of the text
  6. Ensuring that there is no loss of content or functionality when the text resizes and text containers do not resize

Advisory Techniques

  • Providing large fonts by default (future link)
  • Using page-percent for container sizes (future link)
  • Avoiding scaling font sizes smaller than the user-agent default (future link)

    The author won't actually know the font size, but should avoid percentage scaling that results in less than 100%

  • Avoiding justified text (future link)
  • Providing sufficient inter-line and inter-column spacing (future link)
  • Providing different sizes for non-text content when it cannot have an equivalent accessible alternative (future link)
  • Avoiding the use of text in raster images (future link)
  • Using server-side scripts to resize images of text (future link)
  • Scaling form elements which contain text
  • Ensuring that text in raster images is at least 18pt (future link)
  • Scaling text down to 50% (future link)
  • C20: Using ems to set column width so that lines can average 80 characters or less
  • Using CSS to control visual presentation of text
  • Providing a mechanism to allow captions to be enlarged (future link)

Failures