Viewport Size Checker
Check browser viewport dimensions. Run the browser-based check and follow its prompts to review the result.
The viewport is the page area inside your browser window. Resize the window to see the viewport measurements update. Screen and color details are reported by your browser and may be rounded or limited by the device.
Tool guide
About Viewport Size Checker
Read the browser viewport, window, and screen measurements exposed by the page. These values help explain responsive layouts but can change with zoom, browser chrome, orientation, and display scaling.
How to use this tool
- 1Open the page in the browser window you want to inspect.
- 2Read the viewport width and height alongside screen and available-area measurements.
- 3Resize the window or rotate the device to watch the values update.
How the tool works
The page reads values such as `window.innerWidth`, `window.innerHeight`, `window.outerWidth`, `screen.width`, `screen.availWidth`, and `devicePixelRatio`. Viewport dimensions are CSS pixels; device pixels may be estimated by multiplying CSS size by pixel ratio.
Worked real-world example
A 390 CSS-pixel viewport at device pixel ratio 3 corresponds to roughly 1,170 device pixels across, subject to browser reporting.
Common scenarios and use cases
Check a responsive breakpoint, debug a layout, or understand the difference between CSS pixels and a physical screen grid.
Important details and limitations
Browser APIs report logical and security-filtered values, not a complete hardware specification. Zoom, sidebars, display scaling, and browser UI can change measurements; use developer tools for layout debugging.
Check the output unit as well as the number. If the result will be reused in another calculation, retain full precision where possible and round only at the end. For measurements governed by a technical specification, use the standard and tolerance required by that document.
Frequently asked questions
What is the viewport?
It is the page's visible layout area inside the browser window.
Why do screen and viewport sizes differ?
Browser controls and window size reduce the page area.
Are CSS pixels physical pixels?
No. Device pixel ratio relates logical pixels to an estimated device-pixel grid.
About Viewport Size Checker
Check browser viewport dimensions. Run the browser-based check and follow its prompts to review the result.
How to use this tool
Use the controls above to run the check. Results are measured or calculated in your browser. Some device features require browser support, a secure connection, or permission from you.