Your Browser Window Size
The large numbers above show your current browser window width × height in pixels, refreshed instantly as you resize. This is the size that window.innerWidth and window.innerHeight report in JavaScript.
Try it: drag the edge of your window, then snap it to half the screen. Watch the numbers change in real time.
Why Browser Window Size Matters
For web developers and designers, the browser window (viewport) size decides how your layout behaves:
- Responsive design — breakpoints are triggered by window width.
- Testing — you can test 768px, 1024px or 1920px layouts by resizing the window.
- UX — a window that is too narrow makes sites hard to read; too wide makes content lines too long.
Most websites today are designed to work well from 360px (small phones) up to 1920px and beyond (large desktops).
How to Resize Your Browser Window
- Drag any edge or corner of the window to resize it.
- Snap on Windows — press
Win + Left/Right Arrowto fill half the screen. - Snap on Mac — hold the green traffic-light button or hover over it and choose a split layout.
- Full screen — press
F11(Windows/Linux) orCtrl + Cmd + F(Mac). - Maximize — double-click the title bar (Windows) or the window's title bar (Mac).
Frequently Asked Questions
What is window.innerWidth?
It is a JavaScript property that returns the width of the browser window in CSS pixels, excluding scrollbars in most browsers. Websites use it to build responsive layouts.
Why is my browser window smaller than my screen?
The window is only a portion of the full screen. The rest is taken by the taskbar, desktop icons and the space around the window. Press F11 or maximize to use more of the screen.
Can a website detect my window size?
Yes. JavaScript can read the window size (innerWidth/innerHeight) at any moment, which is exactly what this tool does to update the numbers above in real time.