Detect Screen Resolution

The screen resolution reported by window.screen is measured in CSS pixels, which are logical units that browsers use for layout and consistent rendering across devices. Physical pixels are the actual hardware pixels of your display, calculated by multiplying the CSS resolution by the device pixel ratio. On standard displays these two values are identical, but on HiDPI screens (like Apple Retina displays or 4K monitors with scaling enabled) the physical resolution is higher. For example, a 4K monitor at 150% scaling reports 2560×1440 CSS pixels but actually has 3840×2160 physical pixels.

The device pixel ratio, exposed via window.devicePixelRatio, is the ratio between physical hardware pixels and CSS pixels. A DPR of 1x means each CSS pixel maps to exactly one hardware pixel, typical of standard desktop monitors. A DPR of 2x or higher indicates a HiDPI or Retina display, where multiple hardware pixels render each CSS pixel for sharper text and images. The DPR also changes when you adjust the operating system display scaling or the browser zoom level, which is why this value may not be a round number.

No, browsers do not expose the physical dimensions of your display. JavaScript can only read resolutions in CSS pixels, and the true pixel density (PPI) of your monitor is not available to websites. This means a 24-inch and a 27-inch monitor with the same 1920×1080 resolution are completely indistinguishable to a website. The PPI estimate shown in this test is based on the CSS standard assumption of 96 pixels per inch multiplied by the device pixel ratio, which reflects how the browser renders content.

The most common cause is display scaling. If your operating system is set to 125%, 150%, or 200% scaling, the browser reports the scaled CSS resolution rather than the native hardware resolution. For example, a 2560×1440 monitor at 125% scaling reports 2048×1152. Browser zoom has the same effect, since zooming changes the device pixel ratio. Check the Physical Pixels value in the test results, which multiplies the CSS resolution by the device pixel ratio and usually matches your monitor's native resolution.

Yes, screen properties are a common component of browser fingerprinting. Unlike navigator.geolocation, no permission is required to read screen resolution, color depth, device pixel ratio, or touch support, so any website can collect these values silently. Individually these values are not very unique, but combined with other browser characteristics they help build a fingerprint that can identify or track your browser across websites. Some privacy-focused browsers, such as Tor Browser, deliberately report generic screen dimensions to reduce fingerprinting, but this may create issues with some web services.