Monitor PPI Calculator

How the Monitor PPI Calculator works

The formula. PPI = √(width² + height²) ÷ diagonal in inches. For example, a 27-inch 2560 × 1440 monitor has a 2,937-pixel diagonal, so 108.8 PPI. A second example: a 24-inch 1920 × 1080 screen is 2,203 ÷ 24 = 91.8 PPI.

Resolution alone says nothing about sharpness: 1080p is crisp on a phone and coarse on a 32-inch monitor. Pixel density, and better still pixel density combined with viewing distance, is what determines whether you see an image or a grid.

Pixels per inch. PPI is the diagonal pixel count divided by the diagonal size in inches. A 27-inch 1440p monitor has √(2560² + 1440²) = 2938 pixels across its diagonal, giving 109 PPI. That happens to be the density Windows and macOS were designed around at 100% scaling, which is why 27-inch 1440p and 24-inch 1080p (92 PPI) feel "right" without adjustment while a 27-inch 4K (163 PPI) needs 150% scaling to keep text readable.

Dot pitch. The distance between neighbouring pixel centres, 25.4 mm divided by PPI. It is the number monitor manufacturers quote, and smaller means finer. Around 0.23 mm is the comfortable desktop standard; below 0.16 mm the screen is in high-density territory where scaling is essential.

Scaling and effective density. Operating-system scaling makes user interface elements larger so that a high-PPI screen does not shrink text to illegibility. At 150% a 163 PPI display presents interface elements as if it were 109 PPI, but draws them with more pixels, so they are sharper. Integer scaling (100%, 200%) is cleanest; fractional steps (125%, 150%) can blur older applications on Windows. The suggested scaling line picks the conventional value for the density, and the effective PPI it produces.

Pixels per degree. The eye resolves angles, not inches, so the useful sharpness figure is how many pixels fit in one degree of your view. It is 2 × distance × tan(0.5°) × PPI. Sixty pixels per degree corresponds to 20/20 vision resolving a pixel, the threshold Apple used for "Retina"; below about 40 PPD pixels are plainly visible, above 90 most people see no further improvement. The same 27-inch 1440p monitor gives 44 PPD at 50 cm and 62 PPD at 70 cm, which is why sitting slightly further back makes it look sharper. The table applies your distance to eleven common screens, and the calculator also gives the distance at which the current screen reaches 60 PPD.

Choosing a monitor. For desk use at 50 to 70 cm, 27-inch 1440p and 32-inch 4K sit in the sweet spot: sharp enough that pixels disappear, dense enough that no awkward scaling is needed. For competitive gaming where frame rate matters more, a 24-inch 1080p screen viewed slightly further back is still fine, and it puts far less load on the graphics card. Televisions used as monitors need distance: a 42-inch 4K at 60 cm is only 105 PPI and its 60 PPD point is 78 cm away.

PPI calculator: common monitors

Pixel density for common screen sizes and resolutions.

Pixels per inch, dot pitch and suggested scaling by monitor

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