Pixel density is the number of pixels a display can fit into a fixed distance. This is different from “resolution”, which is a simple count of the number of pixels across the entire width and height of a device.
For example, the resolution of a Galaxy S6, is 1440 × 2560 pixels. All of these pixels are crammed into a display that is 5,1inches.
If we compare that to an old-ish VGA desktop monitor, the monitor will have a similar resolution, but a much larger physical size, and thus a significantly lower pixel density.
So, how you will find the PPI of your new Mobile phone?

First, you have to Calculate the diagonal resolution in pixels (d _p).
That happens with the following equation (more info and Solver here), which is based to the Pythagorean Theorem. w _p is width resolution in pixels, and h _p is height resolution in pixels.

Afterwards, you are able to calculate the PPI, by using the d _p you found at the first step, and d _i which is the diagonal size in inches (the number advertised as the size of the display), in the following formula.

There is a list that groups displays by their approximate pixel densities, provided by the Android developer documentation.
• MDPI: Medium density, ~120-160 dots per inch
• TVDPI: Medium High density, ~160-213 dots per inch
• HDPI or HiDPI: High density, ~213-240 dots per inch
• XHDPI: eXtra High density, ~240-320 dots per inch
• XXHDPI: eXtra eXtra High density, ~320-480 dots per inch
• XXXHDPI: eXtra eXtra eXtra High density, ~480-640 dots per inch

Here is an idea! Try to calculate your mobile phone’s screen, your TV and your PC monitor’s PPI, using the links provided above. Then, write a small report in one of our social media pages (listed below), telling us about your experience.