If a layout has android:layout_width="160dp" it renders half the screen on the hdpi Nexus S emulator.
I was expecting the Nexus 4 emulator (xhdpi) and the Nexus 5 emulator (xxhdpi) to scale accordingly, and show me a layout that's taking up half the screen, but they did not. They were a bit less than half (2/5 ish).
What am I missing? I thought that the XML environment always uses a specific screen, so I can base my calculations from there.
If 320dp = 480px / (240dpi / 160) and the Nexus S is hdpi (high) ~240dpi. Makes sense that it's 160dp is half the screen.
Then, the Nexus 5 is xxhdpi (extra-extra-high) ~480dpi with an HD resolution.
So, 1080px / (480dpi / 160) = 360dp!
What? Why?!
Should I avoid using dp when I want to divide my screen assets? Rely on weight and grid?
Indeed, as Budius commented, you cannot rely on dp to divide your screen into segments, since it only helps create a relative understanding of the size so that it reduces the amounts of calculated re-sizing you need to do, but does not effectively replace all unit sizes, such as what a raw percentage would do.
Using weights is the way to go.