1.4.10 Reflow

Many people with low vision zoom their browser to 400 per cent or more. At this magnification, a 1280px-wide page is effectively being viewed at 320px. If content requires horizontal scrolling at this level, it creates a severe usability problem.

This criterion requires that content reflows into a single column at 320 CSS pixels wide (which is equivalent to 400 per cent zoom on a 1280px display) without any loss of content or functionality.

Genuine exceptions include complex data tables, maps, diagrams, and other content that inherently requires two-dimensional navigation to make sense.

Use responsive design principles. Test your site at 320px viewport width or at 400 per cent browser zoom.

Avoid fixed-width layouts. Use fluid grids, max-width, and flexible containers.

Navigation menus that work well on mobile will typically pass this criterion. Desktop-only navigation patterns that do not collapse often fail.

• Fixed-width page that requires horizontal scrolling at 400 per cent zoom
• Sidebar content that overflows and requires scrolling horizontally at high zoom
• Data dashboard with fixed-width panels that do not reflow

This criterion is about content, not about images or other non-text elements. An image that requires horizontal scrolling at high zoom is generally acceptable. Text content that requires horizontal scrolling is not.