Definition: Reflow means content rearranges itself when it is enlarged, rather than running off the screen. Under WCAG 1.4.10 (Level AA), a page must stay readable and usable at a width of 320 CSS pixels without scrolling in two directions – the equivalent of 400% zoom in a window 1280 pixels wide [1].
German: Reflow · Last reviewed: 27 September 2026
Who it helps
Partially sighted people often zoom pages to 200–400%. If they then have to scroll right and back again for every line, they keep losing their place. With reflow they scroll in one direction only – for text, top to bottom. Anyone reading on a small phone benefits too.
What WCAG 1.4.10 requires
- Vertically scrolling content (ordinary web pages): no horizontal scrolling at 320 CSS pixels wide.
- Horizontally scrolling content (vertical scripts, for example): no vertical scrolling at 256 CSS pixels tall.
- Exceptions are content that needs a two-dimensional layout to be understood: maps, diagrams, video, games, presentations, data tables and toolbars [1][2].
Nothing may be lost along the way. Navigation that collapses into a menu button is fine; navigation that is simply cut off is not.
Common mistakes
- Fixed pixel widths, such as
width: 960pxon the content area. - Long words, URLs or lines of code that do not wrap.
- Sticky headers and footers that fill half the screen when zoomed.
- Content that disappears in a narrow window instead of moving elsewhere.
- Zoom switched off with
user-scalable=noin the viewport meta tag.
In code
/* Breaks out of the window at 320 px */
.content { width: 960px; }/* Fits any width */
.content {
max-width: 60rem;
width: 100%;
overflow-wrap: anywhere;
}How to test it
Set the browser window to 1280 pixels wide and zoom to 400%, or narrow the window to 320 pixels in the developer tools. Work through the page: does a horizontal scrollbar appear? Is anything missing? Can you still use menus, forms and dialogs?
How Reviseberg handles it
Reviseberg checks every page a second time at 360 pixels wide. That pass runs the axe-core rules that can fail only in a narrow layout: contrast, target size, zoom disabled in the viewport meta tag (meta-viewport) and scrollable areas a keyboard cannot reach. It does not decide whether a page scrolls horizontally at 320 pixels or loses content. A zoom and reflow agent is not part of Reviseberg today, so Reviseberg treats 1.4.10 as only partly testable by automation – a person tests the rest.
Related terms
Screen magnifier · Text spacing · Target size · Contrast ratio