How is PPI calculated?

PPI = √(width² + height²) ÷ diagonal-in-inches. For a 2560×1440 screen on a 27-inch panel that is √(2560² + 1440²) ÷ 27 ≈ 108.8 PPI.

What is the difference between DPI and PPI?

PPI (pixels per inch) describes screen pixel density, while DPI (dots per inch) describes printer dot density. For displays the terms are used interchangeably, and this tool computes pixels per inch.

What is a good PPI for a monitor?

It depends on viewing distance. Desktop monitors around 90-110 PPI look fine at arm's length, while 'Retina' phones and high-DPI laptops exceed 200-300 PPI because they are viewed up close. Higher PPI means sharper text and images.

Dot pitch is the distance between the centres of neighbouring pixels, equal to 25.4 ÷ PPI millimetres. A smaller dot pitch means a sharper image.

Does a bigger screen always have lower PPI?

For the same resolution, yes — a 27-inch 1440p screen has lower PPI than a 24-inch 1440p screen because the same pixels are spread over more inches. Increasing the resolution alongside the size keeps PPI high.

Why use the diagonal rather than width and height in inches?

Screens are specified by their diagonal size (e.g. a 27-inch monitor), so the calculator combines that with the pixel diagonal — √(width² + height²) — to find density. It then derives the physical width and height for you.

DPI / PPI Calculator

DPI / PPI calculator

Work out the pixel density of any monitor, phone or tablet from its resolution and diagonal size. It is useful for comparing screen sharpness, choosing a monitor, or checking whether a display counts as high-DPI (“Retina”).

How it works

Screens are sold by their diagonal size, so the calculation combines the pixel diagonal with that physical measurement. First it finds the diagonal in pixels with the Pythagorean theorem, then divides by the diagonal in inches:

PPI = √(width² + height²) ÷ diagonal in inches

From the PPI it also derives:

Dot pitch = 25.4 ÷ PPI (millimetres between pixel centres — smaller is sharper)
Active area = width ÷ PPI by height ÷ PPI (the physical display size in inches and centimetres)

Example

A 2560 × 1440 monitor on a 27-inch panel:

diagonal pixels = √(2560² + 1440²) = √(6,553,600 + 2,073,600) ≈ 2937.8 PPI = 2937.8 ÷ 27 ≈ 108.8 PPI

Screen	Resolution	Diagonal	PPI
27” QHD monitor	2560 × 1440	27”	~108.8
24” 1080p monitor	1920 × 1080	24”	~91.8
15.6” 4K laptop	3840 × 2160	15.6”	~282.4

Everything runs in your browser — nothing is uploaded.