Screen PPI Calculator

Horizontal resolution

Vertical resolution

Diagonal, inches

Result

Density, PPI108.8
Assessmentmiddling density, typical for a monitor
Dot pitch, mm0.2335
Pixels merge from, cm80.3
Physical screen size59.8 × 33.6 cm
Megapixels3.69

Resolution means nothing without a diagonal

Works out pixel density from resolution and diagonal, the physical size of a pixel, and the distance at which individual pixels stop resolving.

4K on a phone and 4K on a television are entirely different things. What counts is not the pixel count but the density: how many fall on an inch. It comes from the diagonal in pixels, by Pythagoras, divided by the diagonal in inches.

The second factor is viewing distance. The eye stops resolving detail finer than about one arcminute, and from that comes the distance at which any screen becomes 'retina'. For a monitor that is usually shorter than the distance people actually sit at.

What this calculator shows

Pixel density in PPI and the physical size of one pixel
The distance at which pixels stop resolving
The physical dimensions of the active screen area

What to keep in mind

The calculation assumes square pixels and a rectangular screen without notches or rounded corners.
The resolving threshold is taken as one arcminute, an average for normal vision; sharper eyes do better.

FAQs

What pixel density counts as good?

For a monitor at arm's length, 110 to 140 PPI is enough; a laptop wants 150 to 200; a phone 300 and up, because it is held far closer.

How do I calculate PPI?

Find the diagonal in pixels by Pythagoras and divide by the diagonal in inches. For 2560 × 1440 at 27 inches that is 108.8.

Is 4K worth it at 27 inches?

The difference is visible if you sit closer than 55 centimetres or work with small text. From the usual 70 to 80 centimetres the gain is smaller than people expect.

What is dot pitch?

The spacing between the centres of neighbouring pixels in millimetres. It is 25.4 divided by the PPI: at 108.8 PPI that comes to 0.23 mm.

Worked example

A 27-inch monitor

Input: 2560 × 1440 on a 27″ diagonal

Output: 108.8 PPI, pixels merge from 80 cm

Note: Eighty centimetres is roughly where people sit in front of such a monitor. Which is the whole 4K-at-27-inches argument: at 163 PPI that distance drops to 53 cm.

Useful links

All tools in Photo & Video

Screen PPI Calculator

Result

Related tools

Aspect Ratio Calculator

DPI and Print Size Calculator

Golden Ratio Calculator

Useful links