How to define dimens.xml for every different screen size in android?

You have to create Different values folder for different screens . Like

values-sw720dp          10.1” tablet 1280x800 mdpi

values-sw600dp          7.0”  tablet 1024x600 mdpi

values-sw480dp          5.4”  480x854 mdpi 
values-sw480dp          5.1”  480x800 mdpi 

values-xxhdpi           5.5"  1080x1920 xxhdpi
values-xxxhdpi           5.5" 1440x2560 xxxhdpi

values-xhdpi            4.7”   1280x720 xhdpi 
values-xhdpi            4.65”  720x1280 xhdpi 

values-hdpi             4.0” 480x800 hdpi
values-hdpi             3.7” 480x854 hdpi

values-mdpi             3.2” 320x480 mdpi

values-ldpi             3.4” 240x432 ldpi
values-ldpi             3.3” 240x400 ldpi
values-ldpi             2.7” 240x320 ldpi

For more information you may visit here

Different values folders in android

http://android-developers.blogspot.in/2011/07/new-tools-for-managing-screen-sizes.html

Edited By @humblerookie

You can make use of Android Studio plugin called Dimenify to auto generate dimension values for other pixel buckets based on custom scale factors. Its still in beta, be sure to notify any issues/suggestions you come across to the developer.

Use Scalable DP

Although making a different layout for different screen sizes is theoretically a good idea, it can get very difficult to accommodate for all screen dimensions, and pixel densities. Having over 20+ different dimens.xml files as suggested in the above answers, is not easy to manage at all.

How To Use:

To use sdp:

1. Include implementation 'com.intuit.sdp:sdp-android:1.0.5' in your build.gradle,

2. Replace any dp value such as 50dp with a @dimen/50_sdp like so:

   <TextView
    android:layout_width="@dimen/_50sdp"
    android:layout_height="@dimen/_50sdp"
    android:text="Hello World!" />
   

How It Works:

sdp scales with the screen size because it is essentially a huge list of different dimens.xml for every possible dp value.

See It In Action:

Here it is on three devices with widely differing screen dimensions, and densities:

Note that the sdp size unit calculation includes some approximation due to some performance and usability constraints.

we want to see the changes of required view size in different screens.

We need to create a different values folders for different screens and put dimens.xml file based on screen densities.

I have taken one TextView and observed the changes when i changed dimens.xml in different values folders.

Please follow the process

normal - xhdpi \ dimens.xml

The below devices can change the sizes of screens when we change the normal - xhdpi \ dimens.xml

nexus 5X ( 5.2" * 1080 * 1920 : 420dpi )

nexus 6P ( 5.7" * 1440 * 2560 : 560dpi)

nexus 6 ( 6.0" * 1440 * 2560 : 560dpi)

nexus 5 (5.0", 1080 1920 : xxhdpi)

nexus 4 (4.7", 768 * 1280 : xhdpi)

Galaxy nexus (4.7", 720 * 1280 : xhdpi)

4.65" 720p ( 720 * 1280 : xhdpi )

4.7" WXGA ( 1280 * 720 : Xhdpi )

Xlarge - xhdpi \ dimens.xml

The below devices can change the sizes of screens when we change the Xlarge - xhdpi \ dimens.xml

nexus 9 ( 8.9", 2048 * 1556 : xhdpi)

nexus 10 (10.1", 2560 * 1600 : xhdpi)

large - xhdpi \ dimens.xml

The below devices can change the sizes of screens when we change the large - xhdpi \ dimens.xml

nexus 7 ( 7.0", 1200 * 1920: xhdpi)

nexus 7 (2012) (7.0", 800 * 1280 : tvdpi)

The below screens are visible in " Search Generic Phones and Tablets "

large - mdpi \ dimens.xml

The below devices can change the sizes of screens when we change the large - mdpi \ dimens.xml

5.1" WVGA ( 480 * 800 : mdpi )

5.4" FWVGA ( 480 * 854 : mdpi )

7.0" WSVGA (Tablet) ( 1024 * 600 : mdpi )

normal - hdpi \ dimens.xml

The below devices can change the sizes of screens when we change the normal - hdpi \ dimens.xml

nexus s ( 4.0", 480 * 800 : hdpi )

nexus one ( 3.7", 480 * 800: hdpi)

small - ldpi \ dimens.xml

The below devices can change the sizes of screens when we change the small - ldpi \ dimens.xml

2.7" QVGA Slider ( 240 * 320 : ldpi )

2.7" QVGA ( 240 * 320 : ldpi )

xlarge - mdpi \ dimens.xml

The below devices can change the sizes of screens when we change the xlarge - mdpi \ dimens.xml

10.1" WXGA ( tABLET) ( 1280 * 800 : MDPI )

normal - ldpi \ dimens.xml

The below devices can change the sizes of screens when we change the normal - ldpi \ dimens.xml

3.3" WQVGA ( 240 * 400 : LDPI )

3.4" WQVGA ( 240 * 432 : LDPI )

normal - hdpi \ dimens.xml

The below devices can change the sizes of screens when we change the normal - hdpi \ dimens.xml

4.0" WVGA ( 480 * 800 : hdpi )

3.7" WVGA ( 480 * 800 : hdpi )

3.7" FWVGA Slider ( 480 * 854 : hdpi )

normal - mdpi \ dimens.xml

The below devices can change the sizes of screens when we change the normal - mdpi \ dimens.xml

3.2" HVGA Slider ( ADP1 ) ( 320 * 480 : MDPI )

3.2" QVGA ( ADP2 ) ( 320 * 480 : MDPI )

There are nice libraries which will handle everything and reduce your pain. For using it, just add two dependencies in gradle:

 implementation 'com.intuit.ssp:ssp-android:1.0.5'
 implementation 'com.intuit.sdp:sdp-android:1.0.5'

After that, use dimens like this:

        android:layout_marginTop="@dimen/_80sdp"