Pixel Density (PPI) & Screen Size Calculator
From a diagonal and resolution get PPI, pixel pitch, screen width and height in inches and cm, aspect ratio, megapixels and the distance at which pixels vanish.
The pixel density and physical dimensions of any display, plus the 1-arcminute viewing distance and how big a pixel looks from where you sit.
Example: A 27-inch 2560 × 1440 monitor is 108.8 ppi with 0.233 mm pixels, 23.53 × 13.24 in (59.8 × 33.6 cm), 16:9, 3.69 MP; pixels stop being resolvable beyond 80 cm, and at 60 cm each spans 1.34 arcminutes.
Pythagoras,
then one minute of arc.
How density and size fall out of a diagonal, and what the viewing-distance figures do and do not claim.
Density and dimensions
The diagonal in pixels is √(width² + height²); dividing by the diagonal in inches gives pixels per inch. Everything else follows: pixel pitch is 25.4 mm ÷ PPI, the screen width is the pixel width ÷ PPI, and so on. The calculation assumes square pixels and that the quoted diagonal is the active area — makers round diagonals (a “27-inch” panel may be 26.9), so PPI figures carry that rounding.
The 1-arcminute distance
Normal (20/20 Snellen) acuity resolves detail that subtends one minute of arc. A pixel of pitch p is that small from a distance of p ÷ tan(1′) — about 3,438 pixel pitches — and beyond it a 20/20 eye can no longer pick out individual pixels. That is what the “acuity distance” reports: 80 cm for a 27-inch QHD monitor, 19 cm for a 460-ppi phone. Enter your own viewing distance to see the angular size of a pixel there and the pixels per degree. It is a threshold from a single acuity criterion, not a statement about perceived sharpness, contrast or anti-aliasing; sharper eyes exist.
What it does not do
It does not recommend a monitor, a resolution or a scaling factor, and it does not read your display; enter the figures from the specification. The Aspect Ratio page handles resizing to a target ratio. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Snellen visual acuity — 20/20 defined as resolving detail subtending 1 minute of arc (standard clinical definition)
- NIST SP 811 — the inch (25.4 mm exactly) and SI units
Last reviewed 19 September 2026. How results are checked: How we verify.