Guide · responsive layout
Responsive design testing: which widths to check and what to look for
A page that looks right on your laptop can break on a phone: text clipped, controls overlapping, content that scrolls sideways. This guide lists the widths worth testing, the standard behind the narrowest one, and what to look for at each.
Facts checked
Three widths cover most layout breaks
| Width | Represents | Why check it |
|---|---|---|
| 1440 px | A common laptop or desktop window | Wide layouts expose stretched content, unbalanced columns and unused space. |
| 390 px | A current phone in portrait | Where most layout collapses happen: navigation, tables, fixed bars, long words. |
| 320 px | The narrowest width WCAG reflow tests | WCAG 1.4.10 requires content to work at 320 CSS px without two-dimensional scrolling; it equals 1280 px at 400% zoom. |
What to look for
- Sideways scrolling: the page is wider than the viewport.
- Clipped or overlapping text and controls, especially buttons, badges and long headings.
- Fixed headers, banners and cookie bars that cover the thing you need to tap.
- Tap targets under 24 CSS px (WCAG 2.5.8) that sit close together.
- Tables, code blocks and wide images that force the whole page to scroll. WCAG exempts content that truly needs two dimensions, but the surrounding page should still fit.
How Sybqa checks it
Desktop (1440 px), phone (390 px) and narrow (320 px) audits run in one warm browser, each in an isolated context. Every page or journey gets screenshots and layout checks at all three widths, and the report keys results by route and viewport so a regression at 320 px is not hidden by a pass at 1440 px.
Common questions
Do I need to test every device size?
No. Start with a wide desktop, a current phone width and 320 px. Add widths where your own analytics or your design’s breakpoints suggest a gap.
Does 320 px mean phones are 320 px wide?
Few are. 320 CSS px is the width WCAG uses to model a 1280 px viewport at 400% zoom, so it also protects people who zoom.
Sources
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