Pixel Density (PPI) Calculator
Find the pixel density of any screen from its resolution and diagonal size.
Dot pitch 0.2767 mm/px · 2.07 megapixels
Pixel density is the diagonal resolution in pixels divided by the screen’s diagonal size in inches. For a 1920×1080 panel measuring 24″, the pixel diagonal is √(1920² + 1080²) ≈ 2202.9 px, so 2202.9 ÷ 24 ≈ 92 PPI. Higher PPI means sharper, finer detail at a given viewing distance.
What pixel density means
Pixel density — measured in PPI (pixels per inch) — tells you how tightly packed a screen’s pixels are. Two displays can share the same resolution yet look very different: 1920×1080 on a 24″ monitor is about 92 PPI, but the same resolution on a 6″ phone is over 360 PPI, because the pixels are squeezed into far less space. The higher the PPI, the smaller each pixel and the sharper text and images appear.
PPI vs DPI
The terms are often used interchangeably, and this tool doubles as a DPI calculator, but they are not the same thing. PPI describes pixels on a screen; DPI (dots per inch) describes ink dots a printer lays down. A file has no inherent DPI until you decide a physical print size — DPI only becomes meaningful once pixels are mapped to a page. For displays, PPI is the correct term.
Retina and HiDPI
“Retina” is Apple’s marketing name for displays dense enough that a typical viewer cannot distinguish individual pixels at a normal viewing distance — there is no single fixed number, because it depends on how close you sit. The general concept is called HiDPI: the operating system renders interface elements at 2× (or more) so everything stays crisp instead of tiny. Phones commonly exceed 400 PPI, while desktop monitors reach the same effect at lower densities because you sit farther away.
w and h are the horizontal and vertical resolution in pixels; diagonal is the screen’s diagonal in inches.
- 1 Find the pixel resolution. Note the horizontal and vertical pixel counts, for example 1920 × 1080.
- 2 Compute the pixel diagonal. Use Pythagoras: √(1920² + 1080²) = √4,852,800 ≈ 2202.9 pixels across the diagonal.
- 3 Measure the screen diagonal. This is the advertised size in inches, corner to corner — 24″ for our example.
- 4 Divide to get PPI. 2202.9 ÷ 24 ≈ 91.8, which rounds to about 92 pixels per inch.
- 5 Derive dot pitch if needed. Dot pitch is 25.4 ÷ PPI millimetres per pixel — here 25.4 ÷ 91.8 ≈ 0.277 mm.
Pixel density of common displays
PPI is rounded to the nearest whole number; figures are computed from the listed resolution and diagonal.
| Device | Resolution | Size | PPI |
|---|---|---|---|
| 1080p monitor | 1920×1080 | 24″ | ≈ 92 |
| 1440p monitor | 2560×1440 | 27″ | ≈ 109 |
| 4K monitor | 3840×2160 | 32″ | ≈ 138 |
| 1080p laptop | 1920×1080 | 15.6″ | ≈ 141 |
| HiDPI phone | 2532×1170 | 6.1″ | ≈ 457 |
| 1080p TV | 1920×1080 | 55″ | ≈ 40 |
How to read the result
PPI only matters relative to viewing distance. A 55″ TV at roughly 40 PPI looks perfectly sharp from the sofa, while a phone held at arm’s length needs 300+ PPI to hide its pixels. That is why desktop monitors around 90–110 PPI are comfortable at a keyboard, but the same density on a phone would look coarse.
Two quick sanity checks: dot pitch (25.4 ÷ PPI) is the width of one pixel in millimetres — smaller is finer — and total megapixels (width × height ÷ 1,000,000) tells you how many pixels the panel drives, independent of its physical size. A 4K panel is about 8.3 MP whether it is a 32″ monitor or a 65″ TV.