DPI / PPI Calculator

PPI (Pixels Per Inch) refers to the pixel density of a digital display — how many pixels fit in one inch of screen space. DPI (Dots Per Inch) originally referred to printer resolution — how many ink dots a printer places per inch. In digital contexts the terms are often used interchangeably, but technically PPI is the correct term for screens while DPI applies to printers and physical output. A 4K monitor at 27 inches has roughly 163 PPI.

Apple coined the term Retina Display for screens where individual pixels are indistinguishable at normal viewing distance. The threshold depends on viewing distance: approximately 300 PPI for phones (held ~30cm away), 220 PPI for tablets (~40cm), and 110 PPI for desktop monitors (~70cm). Most modern smartphones exceed 400 PPI, 4K monitors at 27 inches are around 163 PPI, and 4K at 24 inches reaches 184 PPI.

Dot pitch is the physical size of one pixel, measured in millimetres: Dot Pitch (mm) = 25.4 / PPI. A display with 100 PPI has a dot pitch of 0.254mm. Lower dot pitch means higher pixel density and sharper images. Dot pitch is particularly relevant for monitors viewed at close range and for print design where precise physical dimensions matter.

Resolution only describes the total pixel count. A 1920×1080 screen at 24 inches has 92 PPI while the same resolution at 32 inches has 69 PPI — the larger screen has the same number of pixels spread over more physical area, making each pixel bigger and the image less sharp. This is why 4K resolution provides a significant sharpness improvement at 27 inches but a smaller relative improvement at 40+ inches.