Monitor Size, Resolution and Model

Because websites get the size in CSS pixels, not in panel pixels. At 125% Windows scaling one CSS pixel takes 1.25 screen pixels, so 1920 × 1080 becomes 1536 × 864; at 150% it becomes 1280 × 720. Page zoom changes the number once more. The tool takes it apart again: panel pixels, system scaling and page zoom on three separate lines.

The monitor sends the computer its EDID: the model name, its physical size in millimeters and the list of modes. Chrome and Edge on a computer give the page only the name — and only after you allow “Window management”. With that name the tool finds the diagonal, native resolution, maximum refresh rate and HDR in an EDID database. Firefox, Safari and mobile browsers do not report the name; there the size is measured with a bank card.

It depends on the source, which is written next to the number. A card measurement is within about ±0.2″ on a 27-inch screen — a pixel or two of error when fitting the frame. The diagonal from the model is the size the manufacturer wrote into the EDID, usually to the millimeter. An estimate from the resolution is only the most common size for those pixels: for 3440 × 1440 it is almost always 34″, while 2560 × 1080 comes as 29″ and 34″ about equally often, so the tool lists the options.

Most often the rate is simply not switched on: after a new monitor is connected, Windows often stays at 60 Hz until you pick the rate in “Advanced display”. The second reason is the cable or port: an older HDMI cannot carry 144 Hz at high resolution, and on laptops with two graphics chips different ports are wired to different chips. The third is power saving in the browser or laptop, which draws pages less often. When the monitor name is known, the tool compares the measurement with the model maximum and says outright that the rate can go higher.

Yes. A curved panel is an ordinary flat panel that has been bent, and the spec sheet gives its diagonal as if flat. The card measures the pixel pitch where you hold it, so the curve does not affect the result. Only a tape measure can mislead: run it along the surface of the screen, not straight between the corners — the straight line is several centimeters shorter.

That is the “looks like” mode — the interface size you chose in Displays settings. macOS draws the picture twice as large, 2940 × 1912, and scales it down to the real 2560 × 1664 panel of a 13.6″ MacBook Air. The tool recognizes the Mac model from this mode and shows all three numbers: the panel, what the system draws, and what websites see.

21:9 is the marketing name for every ultrawide, and their exact proportions differ: 2560 × 1080 is 64:27 (2.37 : 1), 3440 × 1440 is 43:18 (2.39 : 1), 3840 × 1600 is 12:5 (2.4 : 1). The difference shows when you match a second monitor’s height or watch films shot at 2.39 : 1 — on 43:18 they fill the screen almost without black bars.