Screen Resolution & PPI Calculator

Enter the native resolution and the advertised diagonal. For a 27-inch 1920×1080 display: diagonal pixels = √(1920² + 1080²) = √(3,686,400 + 1,166,400) = √4,852,800 = 2,202.91 px, so PPI = 2,202.91 ÷ 27 = 81.59.

Everything else follows from that density. Physical width = 1920 ÷ 81.59 = 23.53 inches (59.8 cm); physical height = 1080 ÷ 81.59 = 13.24 inches (33.6 cm). Dot pitch = 25.4 ÷ 81.59 = 0.3113 mm. Total pixels = 1920 × 1080 = 2.07 megapixels. Aspect ratio reduces to 16:9.

The last output is the one people are usually really asking about: individual pixels stop being resolvable beyond 1 ÷ (81.59 × tan(1 arcminute)) = 42.1 inches, about 3.5 feet. Most people sit closer than that to a 27-inch monitor, which is exactly why 1080p looks soft at this size and 1440p does not.

Shrink the panel and hold the resolution and the density explodes. For 3840×2160 on a 15.6-inch laptop screen: diagonal pixels = √(3840² + 2160²) = 4,405.81 px, so PPI = 4,405.81 ÷ 15.6 = 282.42, three and a half times the density of the 27-inch 1080p monitor above, from a panel with less than a third of its area.

Physical width = 3840 ÷ 282.42 = 13.60 inches; height = 7.65 inches. Dot pitch drops to 0.0899 mm, and the one-arcminute threshold falls to 12.2 inches. Since almost nobody uses a laptop from closer than about 20 inches, the pixels on this panel are genuinely invisible in normal use, which is the real argument for a high-density laptop screen, and equally the reason a 4K panel on a 32-inch desktop monitor (137.68 PPI, threshold 25.0 inches) is a much more marginal upgrade at typical desk distance.

It is also why such a panel almost always ships with display scaling switched on. At 282 PPI, unscaled interface text renders at roughly a third the physical size it would occupy on the 81.59 PPI monitor.

Dot pitch is pixel density inverted (millimetres per pixel instead of pixels per inch) and is what most display datasheets publish, since the panel industry works in metric. Convert either way with 25.4 ÷ PPI: 0.31 mm and 81.6 PPI describe exactly the same screen, and lower dot pitch means higher density.

Aspect ratio is the resolution reduced by its greatest common divisor, which is why 1920×1080, 2560×1440, and 3840×2160 all reduce to 16:9 and are interchangeable for full-screen content. Phone panels frequently do not reduce cleanly (2556×1179 comes out as 284:131, not any recognisable named ratio) because the resolution is designed around a specific physical panel and cutout rather than a standard. If aspect ratio is all you need, the aspect ratio calculator handles resizing and ratio reduction without the physical-dimension arithmetic.

Physical width and height are worth calculating in their own right. Manufacturers publish the diagonal and the bezel-inclusive case dimensions, but the active panel size (the part that matters for a monitor arm, a recessed mount, or fitting three screens across a desk) usually has to be derived, and the density figure gives it to you directly.

This calculator computes exact geometry from the resolution and diagonal you enter, and it assumes square pixels and a flat rectangular panel. On a curved monitor the advertised diagonal is measured along the curve, so the derived flat width will run slightly wide. Some ultra-wide and phone panels also have rounded corners or a notch, which the raw pixel dimensions ignore.

Density is not sharpness. Two panels at the same PPI can look markedly different depending on subpixel layout (RGB stripe against a PenTile arrangement, where the vendor's stated resolution counts subpixels that are not evenly distributed), as well as anti-glare coating, contrast, and how the operating system renders text. PPI tells you how much detail the panel can hold, not how well it renders any particular content.

The viewing distance figure is a single acuity convention (one arcminute per pixel, roughly 20/20 vision) and nothing more. Real visual acuity varies widely between people and some can resolve detail finer than that threshold, so treat the number as a comparison point between displays rather than a hard limit on what anyone can see.

For proportional resizing and ratio reduction without the physical measurements, use the Aspect Ratio Calculator. If you are working with footage at the resolution you just checked, the Video File Size Calculator turns bitrate and running time into gigabytes, and the Data Storage Calculator sizes a whole photo or video library. To find out what connection speed streaming at a given resolution actually needs, the Bandwidth Calculator works from concurrent streams and per-stream bitrate. Printing is the same idea on paper: the PDF to JPG converter turns PDF pages into images at the DPI you choose, and the JPG to PDF converter can print a photo at its actual size for a given DPI. The DPI number stored inside a JPG or PNG works the same way: it sets the printed size and leaves the pixels alone, and Resize Image can set that tag to 300 DPI, which changes only the file’s header, not its pixels.