Online Tool Store
Browser Zoom Level Tester
Test reflow at zoom levels from 50% to 800%, with a live effective-width calculator and automatic pass/fail overflow detection against the WCAG 1.4.10 320px benchmark.
This works right here on your device — nothing gets sent out.
Simulates zoom by resizing a sample layout to the same "effective CSS width" a real browser would have at that zoom level — a close approximation, not your actual browser's rendering engine. Always confirm on your real site with your browser's own zoom.
100%
Welcome to our store
A short paragraph of body copy to see how text reflows and wraps as the simulated zoom level changes.
How to use it
- Pick a browser window width (1280px matches the standard WCAG 1.4.10 reference point).
- Drag the zoom slider or click a preset from 50% up to 800% — the effective CSS width updates live.
- Watch the pass/fail badges: whether you've reached the 320px WCAG benchmark, and whether the sample layout needs horizontal scrolling at that width.
- Switch to "Fixed-width (common mistake)" mode to see how a single fixed-width element breaks reflow and fails the check.
- Use the same intuition on your own site, then verify with real browser zoom for an accurate result.
FAQ
Does this actually zoom my browser?
No — it resizes a sample layout to the same "effective CSS width" a real browser would have at that window width and zoom level, then checks for real horizontal overflow. It's a close approximation, not your actual browser's rendering engine. For your own site, always confirm with your real browser's Ctrl/Cmd + "+" zoom.
Why does WCAG care about 400% zoom specifically?
WCAG 2.1 success criterion 1.4.10 (Reflow) requires content to reflow into a single column without needing horizontal scrolling at an effective width of 320 CSS pixels — the width you get from a 1280px-wide browser window zoomed to 400%, which is why 1280px and 400% are the standard reference point.
What is "effective width" and how is it calculated?
Effective width is the browser window width divided by the zoom percentage (e.g. 1280px ÷ 400% = 320px). It represents how much CSS pixel space your layout actually has to work with once zoom is applied — the same number a real browser would report to your CSS.
What layout problems typically show up at high zoom?
Fixed-width containers causing horizontal scroll, overlapping navigation items, text that overflows its container, and buttons or cards that get clipped are the most common issues that only appear once zoom passes 150-200%. Switch this tool to "Fixed-width (common mistake)" mode to see exactly how that failure looks.
Does zooming actually shrink the CSS pixel viewport?
Yes. A browser's physical window width in CSS pixels shrinks as zoom increases — that's the mechanism this tool simulates by computing effective width, and it's why a page built with fixed pixel widths can start overflowing horizontally well before 400%.
How we compare
| Feature | Online Tool Store | Reflow-focused testers | URL device-preview tools |
|---|---|---|---|
| Effective-width calculator (window width ÷ zoom %) | ✓ | ✓ | ✗ |
| Live horizontal-overflow pass/fail check | ✓ | ✓ | ✗ |
| Zoom presets up to 800% with live reflow | ✓ | ✓ | ✗ |
| No external URL/embedding needed (works instantly, no X-Frame-Options blocks) | ✓ | ✓ | ✗ |
A quick screening step before opening real browser dev tools and zooming your live page.