PPI means pixels per inch: how many physical pixels fit in one inch of screen. It is calculated by dividing the diagonal resolution in pixels by the diagonal size in inches. Higher PPI means finer detail; around 300 PPI at phone viewing distance looks perfectly sharp to most eyes.

What is the difference between PPI and DPI?

PPI describes screens: physical pixels per inch of display. DPI describes printers: ink dots per inch on paper. They get mixed up constantly because software borrows the term DPI for screen density. When you talk about a monitor or phone, PPI is the technically correct term.

Dot pitch is the distance between the centers of two adjacent pixels, usually given in millimeters. It is the inverse of PPI: dot pitch in mm equals 25.4 divided by PPI. A 92 PPI monitor has a dot pitch of about 0.276 mm; smaller dot pitch means a sharper image.

What is a good PPI for a monitor?

At normal desk distance, 90 to 110 PPI is comfortable standard density, 140 to 160 PPI is noticeably sharp, and above 180 PPI text looks print-like. A 27 inch 1440p monitor sits at 109 PPI, and a 27 inch 4K monitor reaches 163 PPI.

Does a higher PPI always mean a better screen?

No. Past the point where your eyes stop resolving individual pixels, extra density adds battery and GPU cost without visible benefit. Viewing distance decides that point: about 300 PPI at 30 cm, but only about 100 PPI at a meter, which is why TVs get away with far lower densities than phones.

PPI Calculator: Pixels Per Inch, Dot Pitch, Screen Size

How is PPI calculated?

PPI is the diagonal resolution of the screen in pixels divided by the diagonal size in inches. Two steps: first find the pixel diagonal with the Pythagorean theorem, then divide by the physical diagonal.

diagonal_px = √(width² + height²)
PPI = diagonal_px / diagonal_inches

Worked example with a 27 inch 1440p monitor: the pixel diagonal is the square root of 2560 squared plus 1440 squared, which is the square root of 8,627,200, or 2937.2 pixels. Divide by 27 inches and you get 108.8 PPI. Dot pitch is the reverse: 25.4 divided by 108.8 gives 0.233 mm between pixel centers.

PPI vs DPI: they are not the same thing

PPI counts physical pixels per inch of a display. DPI counts ink dots per inch laid down by a printer. The confusion exists because early software used DPI for both, and the habit stuck. It matters in practice: a photo does not have a PPI until it meets a physical surface. A 3000 x 2000 pixel photo printed at 10 x 6.7 inches is 300 DPI; the same file shown on a 163 PPI monitor renders at whatever size the software draws it. If you are preparing images for print or web, our image resizer and image compressor handle the pixel side of that job.

What PPI do real devices have?

Device class	Typical PPI	Example
Budget 24 inch 1080p monitor	92	0.276 mm dot pitch
27 inch 1440p monitor	109	the sweet spot for desktop work
27 inch 4K monitor	163	print-sharp text at desk distance
MacBook Air 13.6	224	2560 x 1664
iPhone 15 Pro	461	1179 x 2556 at 6.1 inches
Galaxy S24 Ultra	505	1440 x 3120 at 6.8 inches
55 inch 4K TV	80	fine at couch distance

Notice the TV at the bottom: 80 PPI sounds terrible next to a phone at 460, yet a 4K TV looks razor sharp from the sofa. Sharpness is always PPI combined with viewing distance, which is what the Retina distance figure in the results is telling you.

Why viewing distance decides everything

Human eyes with 20/20 vision resolve about one arcminute of detail. Converted to pixels, you stop seeing individual pixels when PPI exceeds roughly 3438 divided by the viewing distance in inches. At a phone distance of 12 inches that threshold is about 287 PPI, which is why 300 PPI became the retina benchmark. At a desk distance of 28 inches it drops to about 123 PPI, and at a 3 meter TV distance it is under 30 PPI. Buying more density than your distance can resolve buys nothing visible.

Checking your own screen

The Detect my screen button reads your resolution automatically, including high density displays where the browser reports scaled pixels. You still need to type the diagonal because no browser can read the physical size of a panel. If you want to verify the result physically, calibrate our online ruler with a credit card; the PPI it derives from the card should land within a percent of the number this calculator gives from your specs. If the two disagree by more, your entered diagonal is probably wrong.