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What Is My Window Size?

This page shows your browser's viewport size and updates the moment you drag the window edge, which makes it a quick way to find the exact pixel width where a responsive layout breaks. The viewport is what CSS media queries measure, so these are the numbers that decide whether your mobile, tablet, or desktop rules apply. Alongside the viewport, the page shows the outer window size including browser chrome and the current device pixel ratio, so you can see how much space toolbars are taking. Use it to check where common breakpoints such as 640, 768, 1024, and 1280 pixels land on your machine, to reproduce a layout bug at a specific width, or to confirm what the browser reports after zooming. Nothing is measured on a server; it is all local.

Your viewport size

Detecting…

Drag the edge of the window and this updates live. This is the size CSS media queries measure.

Viewport width
0
Viewport height
0
Window
—including browser chrome
Document
—excluding scrollbars
Pixel ratio
—
Breakpoint
—Tailwind default scale

How to use the what is my window size

  1. Open the page and read the current viewport width and height.
  2. Drag the edge of the browser window and watch the numbers update live.
  3. Resize until you reach the width where your layout changes to find the breakpoint.
  4. Compare the viewport with the outer window size to see how much space browser chrome uses.

Frequently asked questions

Which number do CSS media queries use?
The viewport width, shown here as the inner width. A media query written for a minimum width of 768 pixels applies when the viewport, not the screen or the outer window, reaches 768.
Does the viewport include the scrollbar?
It depends on the browser and platform. Classic desktop scrollbars take a little width away from the viewport; overlay scrollbars, common on macOS and mobile, do not.
Why do the numbers change when I zoom?
Browser zoom changes how many CSS pixels fit in the window. Zooming in reduces the reported viewport size, which is exactly how a zoomed page can trigger a mobile layout on a desktop screen.
Why is the viewport smaller than my screen?
The browser's own toolbars and the operating system's taskbar or dock take space, and the window itself may not be maximised. The screen size tool shows the full display for comparison.

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