Now that we have broadly defined what accessibility is, we need to discuss how to measure it. Accessibility is audited through the Web Content Accessibility Guidelines (WCAG for short), a technical standard currently in version 2.1, planned to reach 2.2 in 2021.

The WCAG offer a dozen guidelines organised under the POUR principles, which stands for Perceivable, Operable, Understandable and Robust. Each guideline is testable through success criteria (a total of over 80 of these), each of them with 3 level of conformance: A, AA and AAA.

For instance, the success criterion related to sufficient color contrast looks like this:

Success Criterion 1.4.3 Contrast (Minimum)
(Level AA)
The visual presentation of text and images of text has a contrast ratio of at least 4.5:1, except for the following:

  • Large Text: Large-scale text and images of large-scale text have a contrast ratio of at least 3:1.
  • Incidental: Text or images of text that are part of an inactive user interface component, that are pure decoration, that are not visible to anyone, or that are part of a picture that contains significant other visual content, have no contrast requirement.
  • Logotypes: Text that is part of a logo or brand name has no contrast requirement.

Generally speaking, reaching a conformance level of A is the strict minimum and required by law, and it is usually encouraged to go for AA. Now, it is not always possible to reach AAA on all success criteria depending on the site, so it’s a nice objective to aim for but shouldn’t be the end goal.

What is important to remember is that even beyond strict specification conformance, there are still a lot of things that can be done to improve accessibility. As we’ve seen yesterday, this is a broad—almost endless topic—so it should never considered done per se and can be actively worked on at all time.

Interestingly enough, the WCAG also apply to mobile interfaces. There is no other significant body of work covering mobile accessibility, so the WCAG can and should be followed (when applicable) for mobile applications, even though they are not written for web technologies.