Last updated: 2026-06-29

PPI / DPI Pixel Density

Pixel density tells you how sharp a screen looks. Two displays can share the same resolution yet appear completely different: a 5-inch phone and a 27-inch monitor might both be 1920×1080, but the phone's pixels are packed far more tightly. This calculator computes pixels per inch (PPI) from a screen's resolution and diagonal size, along with the dot pitch and total megapixels, so you can compare displays on density rather than raw pixel count.

From resolution and size to density

Pixel density is the number of pixels per inch along the screen. To find it, first compute the resolution along the diagonal using the Pythagorean theorem, then divide by the physical diagonal in inches:

$\text{PPI} = \dfrac{\sqrt{w^2 + h^2}}{D}$

where $w$ and $h$ are the horizontal and vertical pixel counts and $D$ is the diagonal size in inches. Because both the pixel count and the physical size enter the formula, density captures something resolution alone cannot: how finely the pixels are spread over the glass.

Dot pitch and megapixels

Two related figures fall out of the same inputs. The dot pitch is the physical distance between adjacent pixel centers — the reciprocal of density, scaled to length:

$\text{dot pitch} = \dfrac{1\ \text{inch}}{\text{PPI}} = \dfrac{25.4\ \text{mm}}{\text{PPI}}$

A smaller dot pitch means finer detail. The total megapixels is simply $w \times h$ divided by a million, a measure of how much the display can show regardless of its size.

Worked example

Consider a 13.3-inch laptop with a 2560×1600 panel. The diagonal resolution is:

Dividing by the 13.3-inch diagonal gives a density of about 227 PPI, with a dot pitch near 0.112 mm and 4.1 megapixels in total. At normal laptop viewing distance that density is high enough that individual pixels are hard to see.

How much density is enough

Beyond the point where pixels become indistinguishable at the usual viewing distance, more density brings no visible benefit while costing power and processing. The threshold depends on distance: a phone held close needs around 300 PPI to look seamless, a laptop about 220, and a television across a room far less. So the useful test is not the raw PPI but whether it is high enough for how the screen is actually viewed. To compare the shape of a display rather than its sharpness, see the Aspect Ratio Calculator.