monitor Screen PPI & Size Calculator star

How the Calculation Works

Screen resolution is a grid of pixels, but the diagonal size is measured in inches on the physical panel — the two only connect through the Pythagorean theorem. PPI = √(width_px² + height_px²) ÷ diagonal_inches: first the diagonal pixel count is found the same way you would find the hypotenuse of a right triangle from its two sides, then that pixel count is divided by the physical diagonal length. A concrete example: a 27-inch monitor at 2560×1440 has a diagonal pixel count of √(2560² + 1440²) ≈ 2937.5 px; divided by 27 inches that gives roughly 108.8 PPI — the sweet spot where text renders sharp at 100% OS scaling. The same 27-inch panel built at 4K (3840×2160) jumps to about 163 PPI, which is why it needs ~150% scaling to keep UI elements a comfortable physical size; a 24-inch 1080p panel sits lower, around 92 PPI, and text visibly softens.

Beyond the single number, the calculator also derives the panel's physical width and height (does it fit the desk?) and the dot pitch in millimeters — the physical distance between the centers of two adjacent pixels — which is useful when comparing two monitors of different sizes that happen to quote the same resolution.

The same math applies to any rectangular display, which is why it is worth running the numbers before buying rather than trusting size and resolution labels alone: two panels advertised as "27-inch, sharp" can differ by 50+ PPI depending on whether the resolution behind them is 1440p or 4K, and that gap is exactly what this calculator surfaces in one step.

What to Know

• PPI is not DPI: PPI (Pixels Per Inch) describes how densely a digital screen packs pixels; DPI (Dots Per Inch) describes how densely a printer lays ink dots on paper. They measure two different physical processes and are not interchangeable, even though the terms are often used as if they were.
• Viewing distance changes everything: PPI alone does not determine perceived sharpness — a 55-inch 4K TV viewed from 3 meters can look sharper than a 27-inch 1440p monitor viewed from 60 cm, because the eye's angular resolution at a given distance is what actually matters, not the raw pixel density.
• "Retina" is a marketing threshold, not a hard rule: displays above roughly 300 PPI at typical desktop or phone viewing distances put individual pixels beyond what the human eye can resolve, so text and images read as continuous rather than pixelated.
• Buying bands: 90-110 PPI is comfortable for desktop monitors at 100% scaling; 140-160+ targets HiDPI/Retina-style rendering at 150-200% scaling; phones run 350-550 PPI because they are held much closer to the eye.
• Dot pitch tells the same story in millimeters: it is simply the physical distance between adjacent pixel centers, so a smaller dot pitch always means a denser, higher-PPI panel — useful when a spec sheet lists dot pitch instead of PPI directly.