Difference and connection between Android dip dp px pt sp

Dip:
Device Independent pixels (device independent pixels). Different devices have different display effects. This is related to the hardware of the device. We recommend that you use this feature to support WVGA, hvga, and qvga, without relying on pixels.

Px:
Pixels (pixels). Different devices have the same display effect. Generally, we use hvga to represent 320x480 pixels, which is usually used.
PT:
Point is a standard length unit, 1pt = 1/72 inch, used in the printing industry, very easy to use;
SP:
Scaled pixels (zoom in pixels). It is mainly used to display the best for textsize in fonts. According to Google's suggestion
It is best to use SP as the unit of font size, and check the source code of textview. We can see that android uses SP as the font size unit by default.

In Android, 1pt is about equal to 2.22sp and above for reference. If the UI can provide the best design in SP units, if the design does not have the concept of SP, then, the developer can take an approximate value by appropriate conversion.

In the past, programmers often designed computer user interfaces in pixels. For example, define a form field with a width of 300 pixels. the spacing between columns is 5 pixels, And the Icon size is 16 × 16 pixels. The problem with this processing is that if you run the program on a new display with a dot (DPI) higher per inch, the user interface will look small. In some cases, the user interface may be small to difficult to see
Content.

The measurement units irrelevant to resolution can solve this problem. Android supports all of the following units.
Px (pixel): the point on the screen.
In (INCHES): the unit of length.
Mm (mm): the unit of length.
Pt (lbs): 1/72 inch.
DP (density-independent pixels): An abstract unit based on screen density. 1dp = 1px on a display at 160 o'clock per inch.
Dip: it is the same as DP and is mostly used in Android/ophone examples.
SP (pixels irrelevant to the scale): similar to DP, but can be scaled based on the user's font size preferences.

Resolution: the number of points on the screen, such as 800x480. It is the display unit of the software, in PX. The density (density) value indicates the number of display points per inch, and the resolution is two concepts. In the APK resource package,

Resources that use the hdpi label when the screen density is 240
Resources that use the mdpi label when the screen density is 160
Ldpi tag resources are used when the screen density is 120.
Generally, Android uses dip to set the length and width, and SP to set the font size. the screen density is 160, 1dp = 1px = 1dip, 1pt = 160/72 SP 1pt = 1/ 72 inch. when the screen density is 240, 1dp = 1dip = 1.5px.

To enable normal display of the current and future display types on the user interface, we recommend that you always use SP as the unit of text size and dip as the unit of other elements. Of course, you can also consider using a vector image instead of a bitmap.

Http://www.eoeandroid.com/forum.php? MoD = viewthread & tid = 76257.