What Is My Viewport Size? Live Browser Size

Your viewport size is shown above and updates the instant you resize the window. The viewport is the visible content area inside your browser, the space left for the page itself after browser chrome, toolbars and scrollbars. It is what responsive CSS actually responds to.

This is almost always the number you want when a design breaks. A layout switches from a multi-column desktop view to a stacked mobile view based on the viewport width, not your monitor's resolution. A large monitor with a narrow browser window behaves like a small screen as far as the page is concerned.

Try dragging the window edge and watch the value change above. That live relationship is exactly what media queries key off, which is why testing at your real viewport beats guessing from your screen specs.

What you should know

Why sites collect it

Responsive sites read the viewport constantly to choose layouts, load correctly sized images, and decide how many columns or menu items fit. Analytics use it to understand the window sizes visitors actually use.

Privacy implications

Viewport size changes as you resize, so it is less stable than screen resolution and therefore a weaker standalone fingerprint. It still contributes when captured at a moment in time, and an unusual window size adds a little entropy.

How to change or hide it

You control the viewport simply by resizing or maximising your browser window. Because it is variable and user-driven, it is one of the less concerning display signals from a tracking standpoint.

Frequently asked questions

Why is my viewport smaller than my screen resolution?

The viewport excludes browser toolbars, the address bar, scrollbars, and any window space you have not filled. It is only the visible page area.

Which size should I test my design against?

Usually the viewport, because responsive breakpoints react to it. Resize your window to your target widths and watch the number above.