What is the difference between ppi vs dpi?

Question

Though I read lot of resources, I am still confused with ppi and dpi. I read value of ppi and dpi of Nexus 6 is 493 and 560 respectively. How it is calculated?

And also what will be the preferred image (full screen) size for Nexus 6 splash screen?

Answer 1

In very simple words:

DPI: Dots per inch, That’s how many droplets of liquid squeeze into an inch of your printed paper.

PPI: Pixels per inch, That’s how many points of light live on an inch of screen.

But it technical terms:

DPI or Dots Per Inch is a measure of spatial dot density initially used in print. It's the number of ink drops your printer can put in an inch . A smaller DPI yields a less-detailed image.

This concept is applied to computer screens under the name PPI for Pixels Per Inch. Same principle: It counts the number of pixels your screen can display per inch. The name DPI is also used in screens.

Windows computers have a default PPI of 96. Mac uses 72, although this value hasn't been accurate since the 80's. Regular, non-retina desktops (mac included) will have a PPI of 72 minimum up to around 120 maximum. Designing with a PPI between 72 and 120 ensures your work is going to be roughly the same size ratio everywhere.

Here’s an applied example: A Mac Cinema Display 27” has a PPI of 109, which means that it displays 109 pixels per inch of screen. The width with bevel is 25.7 inches (65cm). The width of the actual screen is approximately 23.5 inches so 23.5*109~2560, which makes the native screen resolution 2560x1440px.

*I know that 23.5*109 does not equal exactly 2560. It’s actually 23.486238532 inches. It would be more precise with pixels per centimeters, but you get the idea.

For more detail over DPI vs PPI you can visit a very good blog naming guide to DPI by Sebastien Gabriel.

And as per my understanding your looking for some conversion between PPI to DPI then please have a look over this and this.