What is a PPI Calculator?
Resolution alone says nothing about sharpness: 1080p is razor-sharp at 5.5" and coarse at 27". PPI (pixels per inch) is the number that actually compares displays.
Enter resolution and diagonal size to get PPI with a plain-language density class.
Real numbers to compare against: a 24-inch 1080p monitor is 92 PPI, 27 inches at 1440p is 109, the same 27 inches at 4K is 163, a 15.6-inch 1080p laptop is 141, and a 6-inch phone at 2400 × 1080 is 439. Phones run far denser than desktops for one reason: you hold a phone at roughly a third of the distance you sit from a monitor.
Frequently asked questions
Why does this call my monitor “Coarse” when it looks fine?
Because the density class is a fixed PPI band that knows nothing about viewing distance. A 27-inch 1440p panel computes to 109 PPI and a 24-inch 1080p to 92, so both get the Coarse label, even though you sit roughly twice as far from them as from a phone, which halves how large a pixel appears. Compare the PPI figure between screens of the same type and read the label as phone-oriented shorthand.
Does a high-PPI screen need bigger image files?
Yes: a 2x display fills a 400-pixel-wide slot from an 800-pixel source, which is why design assets ship at 2x and 3x. The device’s scale factor, not its raw PPI, picks the multiple, but a high PPI figure is the signal that a 1x asset will look soft.
What is the formula?
PPI = √(width² + height²) ÷ diagonal inches.
What counts as “retina”?
Roughly: pixels invisible at typical viewing distance: ~300+ PPI for phones, ~220 for laptops, ~110 for desktop monitors at arm’s length.
Is higher PPI always better?
Past the invisibility threshold you pay in GPU load and battery for sharpness you cannot see.
Does PPI equal DPI?
PPI is screens; DPI is printer dots. Related concepts, different domains.