Difference between “screen size” and “screen density” in Android?

Question

I have a few questions:

1. What is the screen size?

2. What is the screen density?

3. What is a difference between screen size and screen density?

4. How I can support different densities and different screen sizes in Android?

I have already read the official documentation, but I was unable to understand the difference between screen size and screen density.

Answer 1

• Screen density means how many pixels appear within a constant area of the display, dots per inch = dpi
• Screen size means amount of physical space available for displaying an interface, screen's diagonal, inch
• Screen resolution means number of pixels available in the display, scale-independent pixel = sp
• density-independent pixel = virtual pixel that is independent of the screen density, dp

Density Classes:

Icon Sizes:

• (1) Google documentation says: "Applications should not generally worry about this density; relying on XHIGH graphics being scaled up to it should be sufficient for almost all cases."
• Launcher icons for Android Market: 512x512 px.

Screen Size Classes:

Screen Configuration:

• (1) To emulate this configuration, specify a custom density of 160 when creating an Android Virtual Device that uses a WVGA800 or WVGA854 skin.
• (2) To emulate this configuration, specify a custom density of 120 when creating an Android Virtual Device that uses a WVGA800 or WVGA854 skin.
• (3) This skin is available with the Android 3.0 platform.

Best Practices:

• Use wrap_content, match_parent, or dp units when specifying dimensions in an XML layout file. Except for defining text sizes: sp (scaling depends on user setting)

• Do not use hard coded pixel values in your application code.

• Do not use AbsoluteLayout,use Relative Layout.

• Supply alternative bitmap drawables for different screen densities.

• Provide a launcher icon for xxhdpi, but no other icons.

Answer 2

screen size is about how many pixels you can show on screen.

Density is based on your device real size, if it's small and has a higher resolution, than the density is high cause you show more pixels in less physical space.

1.screen size concerns an absolute number of pixels. (check out wikipedia Image Resolution)

2.Density (aka Pixels per inch - PPI) concerns a relative number of pixels per inch. (check out the wikipedia Pixel Density)

Answer 3

To put it simple:

• Screen size is the physical size of the screen (whether in inch or cm)
• Screen density is the ratio of how many pixels / area of screen size (that's why the unit is dpi, or dots per inch)

Answer 4

Simply put, screen size refers to the size of the screen.This varies from device to device.screen density refers to the amount of pixels in a screen.Both are not independent though as screen size affects screen density.

Answer 5

Please follow the link below for all details :

http://developer.android.com/training/multiscreen/index.html

Also, this link gives very clear concepts:

Application Skeleton to support multiple screen

Answer 6

There are different terms and can't be used interchangeably

density = how many pixels appear within a constant area of the display, dots per inch = dpi or ppi(pixels per inch )

size = amount of physical space available for displaying an interface, screen's diagonal, inch

resolution = number of pixels available in the display, scale-independent pixel = sp