Screen PPI Calculator
Pixels per inch (PPI) measures how densely a display packs its pixels, which determines how sharp it looks. It is found by taking the diagonal resolution in pixels (via the Pythagorean theorem on the width and height pixel counts) and dividing by the diagonal screen size in inches. Enter the horizontal and vertical resolution and the diagonal size, and this calculator returns the PPI, the dot pitch in millimeters, the diagonal pixel count, and the total pixel count. The math is exact geometry, not an estimate.
PPI formula
Diagonal pixels = sqrt(width px^2 + height px^2)
PPI = diagonal pixels / diagonal inches
Dot pitch (mm) = 25.4 / PPI
Total pixels = width px * height px
(25.4 mm per inch)
The diagonal pixel count follows the Pythagorean theorem because the pixel grid is a rectangle.
Display density context
- A 24-inch 1080p monitor is about 92 PPI; a 27-inch 4K display is about 163 PPI.
- Modern smartphones often exceed 400 PPI because they are viewed at close range.
- Apple's Retina marketing term refers to densities where pixels are not individually resolvable at normal distance.
- Dot pitch is the inverse of density: lower dot pitch means a sharper image.
- PPI is about pixel density, distinct from DPI, which describes printer dots.
Screen PPI calculator: frequently asked questions
How do you calculate PPI from resolution and screen size?
First find the diagonal resolution in pixels using the Pythagorean theorem: the square root of width pixels squared plus height pixels squared. Then divide that diagonal pixel count by the screen's diagonal size in inches. PPI equals diagonal pixels divided by diagonal inches.
What is a good PPI for a display?
It depends on viewing distance. Phones held close often exceed 400 PPI, laptops are commonly 100 to 220 PPI, and desktop monitors range from about 90 to 160 PPI. Higher PPI means sharper text and images, but the benefit diminishes once individual pixels are too small to resolve at your distance.
What is dot pitch?
Dot pitch is the physical distance between the centers of adjacent pixels, the inverse of pixel density. It is reported here in millimeters: 25.4 divided by PPI. A higher PPI gives a smaller dot pitch and a sharper image.
Does aspect ratio affect PPI?
PPI depends on the actual pixel width and height and the diagonal inches, not the aspect ratio directly. Two screens with the same diagonal size and total pixels but different aspect ratios will have slightly different PPI because the diagonal pixel count differs.
How is the diagonal pixel count found?
By the Pythagorean theorem, since the pixel grid is a rectangle. For a 1,920 by 1,080 display, the diagonal is the square root of (1,920 squared plus 1,080 squared), which is about 2,202.9 pixels. Dividing by the diagonal inches gives the PPI.
Official sources
- NIST: Unit conversion, inches to millimeters (25.4 mm per inch).
- Video Electronics Standards Association: VESA display standards.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.