官方文档：http://developer.android.com/guide/practices/screens_support.html
The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, which is the baseline density assumed by the system for a "medium" density screen.
The conversion of dp units to screen pixels is simple: px = dp * (dpi / 160).
原文：http://www.cnblogs.com/yarightok/p/5674821.html