What Is My Screen Resolution?

How to read the results

The big number is your screen’s resolution in physical pixels, the figure on a monitor’s spec sheet. The tiles below it show what the browser works with, and the table lists every value with the JavaScript property it comes from. Everything updates live: resize the window, rotate a phone or drag the window to another monitor and the numbers follow. Copy summary puts all of it on your clipboard as plain text for a support ticket or bug report.

CSS pixels and physical pixels

Web pages are laid out in CSS pixels, a unit the operating system scales so that text stays readable on dense screens. The device pixel ratio (DPR) is the number of physical pixels per CSS pixel along each side, so 125% display scaling gives a DPR of 1.25. This page multiplies screen.width and screen.height by devicePixelRatio. When the ratio is fractional, browsers round the CSS size to whole pixels, so the page snaps the product to the nearest standard panel size within that rounding error.

Two cases differ from the spec sheet. A Mac in a scaled mode, such as “looks like 1440 × 900” on a 2560 × 1600 panel, renders at 2880 × 1800 and then shrinks the picture to fit, and 2880 × 1800 is what the page sees. Browser zoom also changes the DPR in Chrome, Edge and Firefox. The page estimates the zoom level and corrects for it in Chromium browsers, but 100% zoom (Ctrl+0, or Cmd+0 on a Mac) gives the most reliable reading.

Screen, viewport and window

• Screen is the whole display; available leaves out the taskbar or Dock.
• Viewport is the area that shows the page, including any scrollbar. CSS media queries such as @media (max-width: 600px) test this width.
• Window is the whole browser window with its tabs and toolbars.

How the refresh rate is measured

Browsers draw at most one frame per screen refresh and run requestAnimationFrame callbacks once per frame. For three seconds the page records each frame’s timestamp, finds the median gap between frames, drops gaps far longer than that (dropped frames) and averages the rest. 60 Hz works out at 16.7 ms per frame and 144 Hz at 6.9 ms.

The reading comes out lower than the monitor’s rating when something holds frames back. Battery saver modes often cap pages at 30 frames per second, and background tabs are paused. Safari holds pages to 60 on 120 Hz ProMotion screens unless the feature flag “Prefer Page Rendering Updates near 60fps” is turned off. Variable refresh rate displays may idle lower. With several monitors, the result is for the one the window is on. If it still reads 60 Hz, check the rate chosen in your system’s display settings and that the cable supports it.

Colour depth, HDR and gamut

Colour depth is screen.colorDepth: 24 bits means 8 bits for each of red, green and blue, 30 bits means 10. Many browsers report 24 whatever the panel. HDR and colour gamut come from the CSS media features dynamic-range and color-gamut. On Windows, HDR usually reads Yes only while HDR is switched on in the display settings.

Common screen resolutions