Dots-per-inch (abbreviated DPI), together with lines-per-inch (LPI) and pixels-per-inch (PPI) are related terms describing display and sensing resolution.
Computer display resolution (not to be confused with image resolution) is commonly measured in either PPI (pixels per inch) or as dotpitch (millimetres per pixel).
dotpitch = 25.4/ppi ⇔ ppi = 25.4/dotpitch
Printing and imaging
Scanner input resolutions are typically not square.