RE: [EXTERNAL] Re: Clarification for Zoom Requirements with WCAG SC 1.4.4 for Desktop and Mobile Devices

Thank you for these clarifications, your explanations make sense to me about why side-to-side scrolling with magnification on mobile devices is not a failure of SC 1.4.4 or 1.4.10.


However, I do think magnification with mobile browser settings is implemented differently than pitch zoom.

Firefox, Chrome and Safari all seem to implement browser zoom for pages in a way that is similar to full page zoom on desktop browsers. As long as components do not have a minimum size that exceeds 160px, content is magnified and made to fit on screen without horizontal scrolling, resulting in a different layout. Pinch zoom just magnifies the original page layout and results in horizontal scrolling.

Attached are screenshots of the Google home page with 100% and 200% magnification set with browser zoom settings. I see the same results for Safari for iOS and Firefox for Android.

It seems that there is an attempt to code major websites in a way that 200% magnification for mobile browsers does not result in side-to-side scrolling. This seems like good UI design for accessibility, but this is not a specific WCAG requirement?


Thank you again for the assistance and clarification, take care.
-Colton

From: Dr. KM Smith, PhD <kmsmithphd@gmail.com>
Sent: Monday, April 27, 2026 4:28 PM
To: Hash, Colton <Colton.Hash@mt.gov>
Cc: w3c-wai-ig@w3.org
Subject: [EXTERNAL] Re: Clarification for Zoom Requirements with WCAG SC 1.4.4 for Desktop and Mobile Devices

Hi Colton,

To answer your question about if mobile device users also need to be able to increase font size by 200% with device or browser settings, as scaling a 320px wide mobile device viewport by 200% full-page zoom without scrolling would effectively mean that all layouts would have to scale down to 160px wide.

I agree with Patrick, and WCAG does not turn SC 1.4.10 into a sweeping160 CSS pixel requirement on mobile. If a 320 CSS pixel mobile viewport is scaled by 200 percent using a page zoom model, the space may feel like about 160 CSS pixels. But SC 1.4.10 Reflow sets the requirement for vertical scrolling content at 320 CSS pixels. W3C also states that [w3.org]<https://urldefense.com/v3/__https:/www.w3.org/WAI/WCAG22/Understanding/reflow.html__;!!GaaboA!rx9bFviQouH2rHQ-ANzD_vN_h9dAMZIz0a3VvDqHDf3eMn5AbaRTqKEuXSqUiYCNe5rYh9C05kXqMh6d2i6J$>if 200 percent zoom results in a viewport smaller than the Reflow sizing requirement, two-dimensional scrolling may occur and that is not a Reflow failure. Which doesnt mean your content gets a pass if  disappears, controls dont work, or users can cant complete functions. Those defectsmay still fail SC 1.4.4, SC 1.4.10 due to viewport size, or other success criteria. The key point is that 160 CSS pixels is not the SC 1.4.10 threshold.

In Partnership,

KM Smith, PhD
Website: www.kmsmithphd.com [kmsmithphd.com]<https://urldefense.com/v3/__http:/www.kmsmithphd.com/accessibility__;!!GaaboA!rx9bFviQouH2rHQ-ANzD_vN_h9dAMZIz0a3VvDqHDf3eMn5AbaRTqKEuXSqUiYCNe5rYh9C05kXqMvByc2Ru$>
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On Mon, Apr 27, 2026 at 5:35 PM Hash, Colton <Colton.Hash@mt.gov<mailto:Colton.Hash@mt.gov>> wrote:
Hi, I am trying to understand the exact requirements for SC 1.4.4 Resize Text and how it relates to SC 1.4.10 Reflow, especially for mobile devices.


Many accessibility training courses mention that it is a requirement for content to scale with font-only zoom up to 200%, which can be tested using Firefox with the zoom text only setting enabled.

However, the W3 Understanding SC 1.4.4 page states,  “Content satisfies the success criterion if it can be scaled up to 200% using at least one text scaling mechanism supported by user agents.” (such as full-page zoom OR font-only zoom )

So to my understanding, a web page could pass SC 1.4.4 if it can scale up to 200% with full-page zoom in a 1280px wide window, even if font-only zoom up to 200% does not work?

This suggests that accommodating font-only zoom is not necessary?


For mobile devices, users also need to be able to increase font size by 200% with device or browser settings. Scaling a 320px wide mobile device viewport by 200% full-page zoom without scrolling would effectively mean that all layouts would have to scale down to 160px wide?

Testing browser zoom with a simple html page with Firefox, Chrome and Safari mobile browsers, all three implement zoom settings as full-page zoom, where both rem and px units are increased with scaling.

Its seems that major mobile browsers do not use font-only zoom?



Taken with SC 1.4.10, I assume that a mobile browser should not scroll in 2 dimensions with browser scaling up to 200%, even though page content is technically below the 320px wide threshold stated in SC 1.4.10?

If mobile browsers do not use font-only zoom, why is scaling down to 160px wide not an explicit requirement?


Thank you for helping to provide more information about these details for WCAG zoom requirements. I will be meeting with the accessibility team of a major GIS software vendor to discuss these requirements, so I want to be sure that I understand SC 1.4.4 correctly. Accommodating 200% zoom in a 320px window will be extremely challenging to meet with interactive GIS software.

Take care,
-Colton Hash


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