Screen resolution checker
Your browser viewport updates live as you resize the window, plus screen resolution, device pixel ratio, orientation and color depth.
Viewport and screen resolution are not the same thing
Your screen resolution is the total size of the display (for example 1920×1080), while the viewport is only the area where the browser actually draws the page: it excludes the address bar, tabs and system bars, and it shrinks whenever the window isn't full screen. When building a responsive website, CSS media queries look at the viewport — not the screen — which is why this page shows it live as you resize the window. It's the number that decides whether your visitors see the desktop or the mobile layout.
What does device pixel ratio mean?
On high-density displays (Retina screens, most modern smartphones) each CSS pixel is rendered using multiple physical pixels: a pixel ratio of 2 means 4 real pixels for every logical one. That's why a phone with a 1170×2532 panel can report a viewport barely 390 pixels wide. The value matters a lot if you prepare images for the web: to look sharp on a ratio-2 display, an image shown at 300 CSS pixels wide should be at least 600 real pixels across.