Pixels per inch

The square shown above is 200 pixels by 200 pixels. To determine a monitor's PPI, measure the width and height, in inches, of the square as displayed on a given monitor. Dividing 200 by the measured width or height gives the monitor's horizontal or vertical PPI, respectively, at the current screen resolution.

Pixels per inch (PPI) or pixel density is a measurement of the resolution of a computer display, related to the size of the display in inches and the total number of pixels in the horizontal and vertical directions. This measurement is often referred to as dots per inch, though that measurement more accurately refers to the resolution of a computer printer. PPI may also be used to describe the resolution of an image scanner or digital camera; in this context, it is synonymous with samples per inch.

Pixels Per Inch Media

The outside of the square shown above is 200 pixels by 200 pixels. To determine a monitor's ppi, set the OS DPI scaling setting at 100% and the browser's zoom at 100%, then measure the width and height, in inches, of the square as displayed on a given monitor.
Display resolution and pixel density

Other websites

All About Photo Printing - The Differences between DPI and PPI

This short article about technology can be made longer. You can help Wikipedia by adding to it.