DPI / PPI Calculator
Calculate the pixel density (PPI) and dot pitch of a display from its resolution and physical screen size.
Results
What is it?
PPI (Pixels Per Inch) measures the pixel density of a display — how many pixels are packed into each inch of screen area. Higher PPI means sharper images. Dot pitch is the inverse: the physical size of each pixel in millimetres.
How to use
Enter your screen horizontal and vertical resolution in pixels, then enter the diagonal screen size in inches (as marketed). The PPI is the diagonal pixel count divided by the diagonal inch measurement.
Example scenario
A 27-inch 2560x1440 (QHD) monitor: PPI = 108.8. A 27-inch 3840x2160 (4K) monitor: PPI = 163.2. Apple Retina threshold at 27 inches (typical arm length) is ~110 PPI — so 4K at 27 inches is definitively Retina, while QHD sits right at the threshold.
Pro tip
Apple originally defined Retina as ~220 PPI for iPhones (~10 inches viewing distance) and ~110 PPI for large displays (~20 inches). The relevant metric is PPI x viewing distance — a 400 PPI TV watched from 10 feet is less sharp in terms of angular resolution than a 200 PPI monitor at 2 feet.