PPI Calculator (Pixel Density)
Work out a display's pixel density from its resolution and diagonal size. Enter the pixel counts and the diagonal, and the calculator returns the PPI, dot pitch, total megapixels, aspect ratio, and the panel's physical width and height.
Low density — the pixel grid can be visible up close.
Pixel density — pixels per inch, or PPI — is how tightly a display packs pixels into physical space. Resolution alone says nothing about sharpness: 1920×1080 across a 27-inch monitor gives big, visible pixels, while the same 1080p on a 13-inch laptop looks noticeably crisper. What matters is the pixel count relative to the panel's size, and that ratio is exactly what PPI measures.
The math is simple geometry: combine the width and height in pixels with the Pythagorean theorem — √(width² + height²) — to get the pixels along the diagonal, then divide by the diagonal in inches. A 27-inch 2560×1440 monitor has √(2560² + 1440²) ≈ 2938 pixels across its diagonal, so 2938 ÷ 27 ≈ 109 PPI. Dot pitch is the same figure as a distance: 25.4 ÷ PPI gives the centre-to-centre pixel spacing in millimetres, so 109 PPI is a 0.233 mm pitch.
How much density you need depends on viewing distance, because what matters is how large each pixel appears from where you sit. A phone held 30 cm away needs far more PPI than a TV across the room — which is why a 55-inch 4K TV looks crisp at around 80 PPI while a flagship phone ships with 450+. It's also why "Retina", Apple's term for pixels too small to distinguish at normal distance, has no single PPI threshold. Rule of thumb: below ~110 PPI the pixel grid is visible up close, and past ~200 PPI individual pixels effectively disappear at arm's length.
Typical pixel densities by device
| Device | Typical PPI | Example |
|---|---|---|
| TVs | 40–90 PPI | 55" 4K TV ≈ 80 PPI — still sharp from sofa distance |
| Desktop monitors (1080p / 1440p) | 80–110 PPI | 27" 1440p ≈ 109 PPI |
| Desktop monitors (4K) | 140–190 PPI | 27" 4K ≈ 163 PPI |
| Laptops | 130–260 PPI | 13.6" MacBook Air ≈ 224 PPI |
| Tablets | 220–280 PPI | 11" iPad Pro ≈ 264 PPI |
| Phones | 400–550 PPI | 6.1" flagship at 1179×2556 ≈ 460 PPI |
PPI vs DPI and dot pitch
PPI (pixels per inch) describes pixels on a screen; DPI (dots per inch) describes ink dots a printer lays on paper. The terms are often used interchangeably — mouse sensitivity is quoted in "DPI" too — but strictly, PPI is the display metric. Dot pitch expresses the same thing as a distance rather than a count, and it's the spec CRT monitors were once sold on: a smaller pitch means a denser, sharper display. A 0.30 mm pitch and roughly 85 PPI describe the same screen two ways.