Pixel Density Calculator

Pixel density, measured in pixels per inch (PPI), describes how many pixels are packed into one inch of screen. Higher PPI means more pixels fit into the same physical space, resulting in sharper, more detailed images. The formula is: PPI = sqrt(horizontal pixels squared + vertical pixels squared) / diagonal inches.

Dot pitch is the distance in millimetres between the centres of adjacent pixels. It is the inverse of PPI: dot pitch (mm) = 25.4 / PPI. A smaller dot pitch means pixels are closer together, resulting in a sharper image. High-resolution displays have dot pitches below 0.1 mm; typical desktop monitors have dot pitches around 0.2-0.3 mm.

Apple defines a 'Retina display' as one where pixels are too small to be individually distinguished at a normal viewing distance. For an iPhone held at 25-30 cm, this threshold is approximately 300 PPI. For an iPad at 38 cm, it is approximately 264 PPI. For a MacBook at 50-60 cm, it is approximately 200 PPI. Different Apple Retina products range from 218 PPI (27-inch iMac) to 460 PPI (iPhone 14 Pro).

Beyond a certain PPI threshold, the human eye cannot distinguish individual pixels at typical viewing distances, so further increases yield diminishing perceptual returns. At smartphone viewing distances (25-30 cm), most people cannot distinguish pixels above approximately 300-350 PPI. For television viewing distances of 2-3 metres, 50-60 PPI is sufficient for most viewers. The 'sweet spot' PPI depends heavily on viewing distance.

Screen PPI and print DPI (dots per inch) are related but different concepts. A screen at 100 PPI displays 100 pixels per inch. When printing an image, you need sufficient source resolution (pixels) to fill the print size at the printer's DPI. For photo printing at 300 DPI, a 6x4 inch print needs at least 1800x1200 pixels. Screen PPI directly affects sharpness of the display; print DPI affects physical print sharpness.