Screen PPI Calculator

This calculator turns a display's resolution and screen size into pixel density (PPI), dot pitch (the distance between pixel centers, in millimeters) and the viewing distance beyond which a person with normal vision can no longer pick out individual pixels. It also gives the total pixel count, which is what your graphics card has to drive.

Use it when comparing monitors of different sizes, deciding whether a 4K screen is worth it at 24 or 27 inches, or checking how close you can sit to a TV. The diagonal must be the visible screen size the manufacturer quotes, not the outer bezel. If you only know the ratio and one dimension, work out the other with the aspect ratio calculator first.

PPI describes sharpness, not image quality as a whole: panel type, contrast, scaling in your operating system and the content's own resolution all change what you see. A 4K screen showing 1080p video still shows only 1080p detail.

The diagonal pixel count comes from Pythagoras' theorem, so the formula works for any aspect ratio, including 21:9 ultrawides and 3:2 laptops. The "retina" distance assumes 20/20 vision, which resolves detail of about one arcminute; this is the same idea Apple used when it introduced the term. People with sharper than 20/20 vision can see pixels from a little farther away. For screens with non-square pixels (rare outside older video formats) the formula does not apply.

Figures below use the formula on this page with the stated resolution and diagonal. Phone figures vary by model, so check the exact panel size before comparing.

Sharpness depends on pixels per degree of your vision, not PPI alone, so distance matters as much as density. Rough guide for 20/20 vision:

• Phones (10–12 in away): around 300 PPI or more before pixels disappear, which is why phones sit at 400–500 PPI.
• Laptops (18–20 in): roughly 170–190 PPI for a pixel-free look; 1080p on a 13–14 inch screen is close.
• Desktop monitors (24–30 in): 110–140 PPI is where most people stop noticing pixels at 100% scaling; above that, you gain smoothness but need OS scaling.
• TVs (6–10 ft): about 30–50 PPI is enough, which is why 4K benefits appear mainly on large screens or close seating.

To check a specific setup, compare the calculator's retina distance with how far your eyes actually are from the screen. If you sit closer than that figure, a higher resolution will look sharper.

High-PPI monitors are usually run with operating-system scaling (125%, 150% or 200%) so text stays the same physical size. Scaling at a whole-number factor such as 200% on a 4K screen gives the cleanest result; fractional scaling can blur some older applications.

Two screens with the same PPI can still look different. Subpixel layout (RGB stripe versus the triangular or pentile layouts on some OLED panels) affects how crisp text edges look, and a matte coating slightly softens fine detail. For gaming, more pixels also mean more work for the graphics card: 4K is four times the pixel count of 1080p, so frame rates fall accordingly.