Find the monitor’s diagonal size in inches
Find the horizontal resolution in pixels
Find the vertical resolution in pixels
Calculate pixel diagonal: square root of (horizontal pixels² + vertical pixels²)
Divide pixel diagonal by diagonal size in inches
Result = PPI
Formula: PPI = sqrt(width² + height²) / diagonal inches
Example: 1920×1080 on a 24-inch monitor = sqrt(1920² + 1080²) / 24
Use an online PPI calculator if you want a quick result