How do dp, dip, dpi, ppi, pixels and inches relate?

Question

I was reading dp, dip, px, sp measurements, but I still have some questions about dp/dpi vs ppi vs px vs inch. I am not able to compare them... is an inch the largest?

Answer 1

How do dp, dip, dpi, ppi, pixels and inches relate?

For the purpose of android development:

dp = dip
dpi = ppi
inch x dpi = pixels
dp = 160 x inch
dp = 160*pixels/dpi

So, on a 160dpi phone (mdpi):

2 inches = 320 dp
2 inches = 320 pixels

On a 180 dpi phone:

2 inches = 320 dp
2 inches = 360 pixels

Note that 2 inches is ALWAYS 320dp, independent of screen size. A dp is a physical distance of 1/160th of an inch.

The dp to pixels formula is interesting:

dp = 160*pixels/dpi

Is equivalent to:

dp = pixels/(dpi/160)

dpi/160 is an interesting factor. Its the relative density compared to android's mdpi bin and the amount you must scale your graphics by for the various resource bins. You'll see that factor mentioned a few times on this page, 0.75 being the factor to ldpi.