Reflow (1.4.10)

Content must reflow to fit within a viewport width of 320 CSS pixels without requiring horizontal scrolling, except for content that requires two-dimensional layout (data tables, toolbars, maps).

WCAG Reference

Applies to: WCAG 2.1, WCAG 2.2 Introduced in: WCAG 2.1 | Level: AA | Read the official specification →

What this rule checks

The scanner identifies content that causes horizontal scrolling at 320px viewport width (equivalent to 400% zoom on a 1280px desktop display).

Why it matters

Users with low vision who zoom to 400% or more should not have to scroll horizontally to read each line of text. Horizontal scrolling makes reading extremely difficult and slow.

Common failure patterns

fixed-width layouts or containers that do not respond to viewport changes
wide data tables presented as the primary reading content without a scrollable wrapper
images or embedded media with fixed pixel widths that overflow the viewport
multi-column layouts that do not collapse to a single column at narrow widths

Remediation guidance

use responsive CSS (relative units, max-width, flexbox/grid) to allow single-column reflow
wrap wide tables in a scrollable container so the rest of the page still reflows
set images to max-width: 100% so they scale within their container
test at 320px viewport width (or 400% zoom) and fix any horizontal overflow