PPI Calculator (Pixel Density)
Work out a display's pixel density from its resolution and diagonal size. Enter the horizontal and vertical pixel counts and the diagonal in inches or centimetres, and the calculator returns the pixels per inch (PPI), the dot pitch, the total megapixels, the reduced aspect ratio, and the physical width and height of the panel.
Low density — the pixel grid can be visible up close.
How PPI is calculated
Pixel density is the diagonal pixel count divided by the diagonal size in inches. Take the width and height in pixels, combine them with the Pythagorean theorem — the square root of (width² + height²) — to get the number of pixels along the diagonal, then divide by the diagonal measured in inches. A 27-inch monitor at 2560×1440 has √(2560² + 1440²) ≈ 2938 pixels across the diagonal, so 2938 ÷ 27 ≈ 109 PPI. From the PPI you also get the dot pitch, the centre-to-centre distance between pixels, as 25.4 ÷ PPI in millimetres.
Why pixel density matters
Higher pixel density packs more pixels into the same physical space, so edges and text look sharper and the pixel grid is harder to see. But density only tells half the story: what your eye actually resolves also depends on viewing distance. A phone held 30 cm away needs far more PPI to look smooth than a TV watched from across the room. That is why a 55-inch 4K TV can look crisp at around 80 PPI while a phone screen is expected to exceed 400 PPI — you sit much closer to the phone.
Typical pixel density for phones, monitors and TVs
- Phones: roughly 400–500+ PPI. Modern flagships pack a very high density because you hold them close to your eyes.
- Laptops and tablets: about 150–260 PPI, higher on "Retina" and high-DPI panels.
- Desktop monitors: around 90–110 PPI for common 1080p and 1440p displays, and roughly 140–190 PPI for 4K models at 27–32 inches.
- TVs: often 40–90 PPI. The large size spreads the same 4K pixels thinly, which still looks sharp from a normal sofa distance.
PPI vs DPI, dot pitch and "Retina"
PPI (pixels per inch) describes pixels on a screen; DPI (dots per inch) describes ink dots on a printed page. The terms are often used interchangeably, but strictly PPI is the display metric. Dot pitch is the same information expressed as a distance rather than a count: a smaller pitch means a denser, sharper display. "Retina" is Apple's marketing name for a screen whose pixels are too small to distinguish at a typical viewing distance — there is no single PPI threshold, because it depends on how far away the display is normally used.
Related calculators
Working out a display's geometry? The Aspect Ratio Calculator reduces and converts width-to-height ratios, and the Retina Display Calculator checks whether a screen is pixel-sharp at a given viewing distance.