Recommended workflow
- 1. Enter the URL you want to test.
- 2. Choose a viewport preset or type a custom width and height.
- 3. Open the target page directly if the preview is blocked by iframe security headers.
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Responsive preview tool
Responsive Website Tester
Preview a URL inside common viewport presets and custom sizes for quick responsive checks.
Preview note
Some websites block iframe previews using security headers.
Selected viewport
390 × 844
Target URL
https://screenmetriclab.com
Preview ready
Load https://screenmetriclab.com at 390 × 844. If the preview stays blank, the target site may block iframe previews.
Open URL in new tabHow to use it
Responsive Website Tester guide
Use the responsive website tester to preview a page at common mobile, tablet, laptop, and desktop viewport sizes. It helps catch layout issues before opening a full device lab or browser emulator.
Limitation: Some websites block iframe previews with security headers. When that happens, use the selected viewport size as your target and open the URL in a browser responsive mode.
Practical examples
Use 390 by 844 for a common modern mobile viewport check.
Use 768 by 1024 for tablet portrait layout checks.
Use 1366 by 768 and 1440 by 900 for laptop and desktop QA notes.
Frequently asked questions
Why is the responsive preview blank?
The target site may block iframe previews using security headers. Use the open URL button and test the same viewport in your browser instead.
What viewport sizes should I test first?
Start with one mobile width around 390px, one tablet width around 768px, one laptop width around 1366px, and one desktop width around 1440px.
Is this the same as testing on real devices?
No. It is a quick viewport preview. Real device testing is still useful for touch behavior, browser UI, performance, and safe-area issues.
Helpful references
Related responsive testing resources
Use these tools to pair viewport previews with live screen size, device references, and display comparisons.
Check live values
Live screen details
Check live screen resolution, viewport size, DPR, browser, OS, and display details.
Viewport Size Checker
Measure the CSS viewport width and height your webpage can use right now.
Screen Resolution Checker
Find the physical pixel grid reported by your current display.
DPR Checker
Check device pixel ratio for retina assets, screenshots, and layout debugging.
Measure and compare
Screen Size Calculator
Calculate monitor width, height, area, aspect ratio, and PPI from diagonal size and resolution.
How to Measure Screen Size
Measure a monitor, laptop, TV, phone, or tablet diagonally without including the bezel.
27-Inch 4K Monitor
Check 27-inch 4K panel dimensions, 163.18 PPI, pixel pitch, and scaling behavior.
Screen Size Comparison
Compare phones, tablets, laptops, monitors, and TVs by viewport, resolution, DPR, and PPI.
Device references
Device Viewport Database
Search viewport, DPR, resolution, diagonal size, and PPI references.
iPhone Viewport Sizes
Open iPhone CSS viewport, screen size, resolution, and DPR references.
MacBook Screen Sizes
Compare MacBook logical viewport, resolution, DPR, diagonal size, and PPI.
Monitor Screen Sizes
Review 1080p, QHD, 4K, and ultrawide monitor references.
Guide collection
Related guides
Use these supporting guides to understand the tool result and next testing steps.
Related tools
Continue with another ScreenMetricLab utility.
Need more screen sizing help? Explore device viewport sizes, compare popular screens, or read our screen and viewport guides.