Pixel density tells you how sharp a screen looks. Two monitors can both be “4K,” but a 27-inch model packs its pixels far more tightly than a 43-inch one. This calculator turns a resolution and a diagonal size into pixels per inch (PPI), plus the dot pitch, the physical width and height of the screen, and the viewing distance beyond which individual pixels disappear.
How to use the PPI calculator
- Enter the horizontal and vertical resolution in pixels, such as 2560 and 1440.
- Enter the diagonal screen size and choose inches or centimeters.
- Read the PPI on the tape, with dot pitch, total pixels, physical size, aspect ratio and the “retina” viewing distance below it.
PPI formula
The viewing distance at which one pixel subtends one arcminute — the resolving limit of 20/20 vision — is
Worked example
A 27-inch monitor with a 2560 × 1440 resolution:
- Diagonal pixels: √(2,560² + 1,440²) = √8,627,200 ≈ 2,937.21.
- PPI: 2,937.21 ÷ 27 ≈ 108.79.
- Dot pitch: 25.4 ÷ 108.79 ≈ 0.2335 mm.
- Physical size: 2,560 ÷ 108.79 ≈ 23.53 in wide and 1,440 ÷ 108.79 ≈ 13.24 in tall.
- Pixels blend together at about 3,438 ÷ 108.79 ≈ 31.6 inches.
At a typical desk distance of 24–30 inches, a sharp-eyed viewer can just make out the pixels; the same panel at 4K (3840 × 2160) would be 163 PPI, with a blend distance of about 21 inches.
Pixel density of common screens
| Screen | Resolution | PPI |
|---|---|---|
| 24″ monitor | 1920 × 1080 | 91.8 |
| 27″ monitor | 2560 × 1440 | 108.8 |
| 27″ monitor | 3840 × 2160 | 163.2 |
| 15.6″ laptop | 1920 × 1080 | 141.2 |
| 13.3″ laptop | 2560 × 1600 | 227.0 |
| 6.1″ phone | 2532 × 1170 | 457.3 |
| 65″ TV | 3840 × 2160 | 67.8 |
What the numbers mean in practice
Viewing distance changes everything
A 65-inch 4K TV has a lower PPI than a budget laptop, yet looks razor-sharp from the couch because you sit 8 or 9 feet away. Its blend distance is only about 51 inches. Pixel density only matters relative to how far away your eyes are, which is why phones need several hundred PPI and billboards get by with a few.
Scaling and text size
High-PPI monitors make text tiny at 100% scaling. Operating systems compensate with display scaling (150% or 200%), which keeps text a comfortable size while drawing it with more pixels, so it looks smoother. A 27-inch 4K monitor at 150% gives roughly the workspace of a 2560 × 1440 screen with sharper text.
PPI is not print DPI
An image’s “300 DPI” setting only matters when printing; on a screen, every image is displayed at the monitor’s own PPI. To plan print sizes, use the DPI option in the image resize calculator.
To find a screen’s width and height from its diagonal and aspect ratio alone, use the screen size calculator.
Frequently asked questions
How is PPI calculated?
Find the diagonal resolution in pixels with the Pythagorean theorem, √(width² + height²), and divide by the diagonal size in inches. A 27-inch 2560 × 1440 monitor has √(2560² + 1440²) ≈ 2,937.2 pixels across its diagonal, so 2,937.2 ÷ 27 ≈ 108.79 PPI.
What is a good PPI for a monitor?
Around 90–110 PPI is typical for desktop monitors viewed from about 24–30 inches. Around 140–220 PPI looks crisp at laptop distances, and phones viewed close up usually exceed 400 PPI.
What is the difference between PPI and DPI?
PPI counts pixels on a screen or in a digital image. DPI (dots per inch) strictly describes a printer's ink dots. People often use DPI loosely for both, as in '300 DPI images for print'.
What does 'pixels blend together at' mean?
It is the distance at which one pixel spans one arcminute of your view, the detail limit for 20/20 vision. Beyond that distance a person with normal vision cannot pick out individual pixels; closer than that, they can.