Android Layout – Understanding Relations Between dip, px, and dpi

androidlayoutresolution

If, in a layout xml file, I set the size to be, for example 12dip. Will that always be 12px in mdpi and so 18px in hdpi?

So is dip always true for mdpi and will scale accordingly for other densities?

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That question is fully covered by official documentation. Relations between dip, px and dpi are covered by this section.

Quote:

Density-independent pixel (dp)

A virtual pixel unit that applications can use in defining their UI, to express layout dimensions or position in a density-independent way.

The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, the baseline density assumed by the platform (as described later in this document). At run time, the platform transparently handles any scaling of the dp units needed, based on the actual density of the screen in use. The conversion of dp units to screen pixels is simple: pixels = dps * (density / 160). For example, on 240 dpi screen, 1 dp would equal 1.5 physical pixels. Using dp units to define your application's UI is highly recommended, as a way of ensuring proper display of your UI on different screens.

So the statement:

that always be 12px in mdpi and so 18px in hdpi

seems to be correct, according to the docs.

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Android – Difference Between px, dip, dp, and sp

From the Android Developer Documentation:

px
Pixels - corresponds to actual pixels on the screen.
in
Inches - based on the physical size of the screen.
1 Inch OR 2.54 centimeters
mm
> Millimeters - based on the physical size of the screen.
pt
> Points - 1/72 of an inch based on the physical size of the screen.
dp or dip
> Density-independent Pixels - an abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi screen, so one dp is one pixel on a 160 dpi screen. The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion. Note: The compiler accepts both "dip" and "dp", though "dp" is more consistent with "sp".
sp
> Scaleable Pixels OR scale-independent pixels - this is like the dp unit, but it is also scaled by the user's font size preference. It is recommended you use this unit when specifying font sizes, so they will be adjusted for both the screen density and the user's preference. Note, the Android documentation is inconsistent on what sp actually stands for, one doc says "scale-independent pixels", the other says "scaleable pixels".

From Understanding Density Independence In Android:

Density Bucket	Screen Density	Physical Size	Pixel Size
ldpi	120 dpi	`0.5 x 0.5 in`	`0.5 in * 120 dpi = 60x60 px`
mdpi	160 dpi	`0.5 x 0.5 in`	`0.5 in * 160 dpi = 80x80 px`
hdpi	240 dpi	`0.5 x 0.5 in`	`0.5 in * 240 dpi = 120x120 px`
xhdpi	320 dpi	`0.5 x 0.5 in`	`0.5 in * 320 dpi = 160x160 px`
xxhdpi	480 dpi	`0.5 x 0.5 in`	`0.5 in * 480 dpi = 240x240 px`
xxxhdpi	640 dpi	`0.5 x 0.5 in`	`0.5 in * 640 dpi = 320x320 px`

Unit	Description	Units Per Physical Inch	Density Independent?	Same Physical Size On Every Screen?
px	Pixels	Varies	No	No
in	Inches	1	Yes	Yes
mm	Millimeters	25.4	Yes	Yes
pt	Points	72	Yes	Yes
dp	Density Independent Pixels	~160	Yes	Yes
sp	Scale Independent Pixels	~160	Yes	No

More info can be also be found in the Google Design Documentation.

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Android – Difference Between px, dip, dp, and sp

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