What is the difference between viewport size and screen resolution?

The viewport is the visible area inside the browser window after toolbars and scrollbars, while screen resolution is the whole display. A maximised window is usually smaller than the screen.

Which breakpoints does it use?

It reports the common Tailwind/Bootstrap-style breakpoints — sm 640px, md 768px, lg 1024px, xl 1280px and 2xl 1536px — to help with responsive layout work.

Is any data collected?

No — the size is read from your own browser with window.innerWidth and innerHeight and never leaves your device.

Viewport Size Checker

Live browser viewport size, breakpoint and scrollbar width.

Viewport size checker

See your browser viewport in CSS pixels in real time, along with the active responsive breakpoint, orientation, scrollbar width, device pixel ratio and the physical viewport in device pixels.

Resize the window or rotate your phone and every value updates instantly — ideal for responsive design and media-query testing. All measurements stay in your browser.