Screen PPI Calculator guide
Enter a screen's resolution and diagonal size to calculate pixels per inch, dot pitch, width and height, total megapixels, and how far away you need to sit before individual pixels blend together.
The formulas behind the numbers
Diagonal resolution in pixels comes from the Pythagorean theorem: √(width² + height²). Divide that by the advertised diagonal in inches and you have pixels per inch. Everything else follows from PPI.
Dot pitch = 25.4 ÷ PPI, in millimeters, because an inch is exactly 25.4 mm. Physical width = horizontal pixels ÷ PPI, and height = vertical pixels ÷ PPI. Aspect ratio divides both dimensions by their greatest common divisor, so 2560 × 1440 reduces to 16:9. The blend distance is the point where one pixel spans 1 arcminute of your field of view, which works out to 1 ÷ (PPI × tan(1/60°)), or about 3,438 ÷ PPI inches.
Worked example: choosing a 27-inch monitor
27-inch 1080p: √(1920² + 1080²) = 2,202.9 pixels, ÷ 27 = 81.59 PPI. Dot pitch 0.3113 mm. Pixels blend at about 42 inches, but you sit around 24 to 30 inches from a desk monitor, so you can see them. Text looks fuzzy.
27-inch 1440p: 2,937.2 ÷ 27 = 108.79 PPI, dot pitch 0.2335 mm, blend distance 31.6 inches. At a normal desk distance it looks clean at 100% scaling, which is why this is the long-running sweet spot for gaming and general work.
27-inch 4K: 4,405.8 ÷ 27 = 163.18 PPI, blend distance 21.1 inches. Pixels are invisible from your chair. The catch is that at 100% scaling everything is tiny, so Windows and macOS usually run it at 150% or more, which gives you the workspace of a 1440p screen with much sharper text.
All three are 23.53 by 13.24 inches of actual glass. Same size, very different sharpness.
Reference values for common screens
24-inch 1080p: 91.79 PPI. 32-inch 4K: 137.68 PPI. 15.6-inch 1080p laptop: 141.21 PPI. 65-inch 4K TV: 67.78 PPI. An iPhone 15 panel, 2556 × 1179 at 6.1 inches, computes to 461 PPI; Apple lists 460, and the gap comes from the diagonal being rounded in marketing specs.
That rounding matters for every screen. A "27-inch" monitor might measure 26.9 inches of viewable area, and TVs are often a fraction of an inch smaller than their class size. For exact numbers, use the viewable diagonal from the spec sheet.
Viewing distance is half the story
Sharpness depends on how many pixels land in each degree of your vision, not PPI alone. A phone at 460 PPI held 11 inches away and a TV at 68 PPI viewed from 8 feet can both look flawless. That is why the calculator shows the blend distance: sit farther than it and you have effectively reached the limit of 20/20 vision.
Many people with good eyesight can see a little better than 20/20, and fine text and high-contrast edges show aliasing past the 1 arcminute line. Treat the blend distance as a practical threshold, not a hard physical limit.
PPI for designers and developers
CSS does not care about physical PPI. A CSS pixel is a reference unit, and the browser maps it to device pixels using the device pixel ratio: 1 on a standard 1080p monitor, 2 on most MacBooks and many phones, 3 on high-end phones. A 400-pixel-wide image looks sharp on a 2x screen only if you serve an 800-pixel version, which is what srcset is for.
For print, 300 PPI at final size is the standard for photos. An image headed for an 8 × 10 inch print needs 2400 × 3000 pixels to hit that. Screen PPI has nothing to do with it; the image's pixel count and print size decide everything.
Common mistakes
Swapping width and height does not change PPI, but entering the wrong diagonal does. Using a 16:9 resolution with an ultrawide's diagonal gives a wrong answer; ultrawides like 3440 × 1440 at 34 inches are 21:9 (109.68 PPI).
Comparing PPI across very different distances. A 13-inch laptop at 220 PPI is not "twice as sharp" as a 27-inch 4K at 163 PPI in practice, because you sit closer to the laptop.
Frequently asked questions
How is PPI calculated?
PPI = √(width² + height²) ÷ diagonal inches. A 27-inch 2560 × 1440 monitor has a 2,937.2-pixel diagonal, so 2,937.2 ÷ 27 = 108.79 PPI.
What is a good PPI for a monitor?
Around 90 to 110 PPI looks sharp at normal desk distance with no scaling, which is why 24-inch 1080p (92 PPI) and 27-inch 1440p (109 PPI) are popular. 27-inch 4K at 163 PPI is noticeably crisper but usually needs 150% scaling.
Is 1080p good enough on a 27-inch monitor?
It is only 81.6 PPI, so text looks soft and pixels are visible within about 42 inches. For 27 inches, 1440p or 4K is the better choice.
What is the difference between PPI and DPI?
PPI counts pixels on a screen or in a digital image. DPI counts ink dots a printer lays down per inch. People often use DPI loosely for both, but for displays PPI is the correct term.
What is dot pitch?
The distance between the centers of adjacent pixels, usually in millimeters. It is 25.4 ÷ PPI. A 24-inch 1080p monitor has a 0.2767 mm dot pitch; smaller numbers mean a finer, sharper image.
What PPI is a Retina display?
Apple does not use a fixed number. Retina means pixels are invisible at typical viewing distance: roughly 300+ PPI for phones held about 10 to 12 inches away and around 220 PPI for laptops viewed from farther back.
Does a TV need high PPI?
No. You sit much farther away. A 65-inch 4K TV is only 67.8 PPI, but its pixels blend at about 51 inches, so from a typical 7 to 9 foot couch distance it looks perfectly sharp.
Is data uploaded?
Everything runs in your browser. Nothing you enter is uploaded to a server or stored by us.
What resolution do I need for a sharp 32-inch monitor?
4K (3840 × 2160). At 32 inches that is 137.68 PPI, sharp at desk distance. 1440p at 32 inches is only 91.79 PPI, similar to a 24-inch 1080p screen.
How many PPI do I need for printing photos?
300 PPI at the final print size is the standard for photo quality. A 4 × 6 inch print needs 1200 × 1800 pixels; an 8 × 10 needs 2400 × 3000.