As screen displays are built with dots of light and pixels and don't have a fixed dimension, we like to measure the screens' sizes using the Pixels Per Inch (PPI). For instance, your phone has 5 inches, and your monitor display has 42 inches. Both of them have a resolution of 1920x1080, but since the phone has a smaller size, it will have a higher PPI than the monitor display. Not to be confused with his brother Dots Per Inch, because when the time comes to print something, the pixel ceases to exist.