How to use Percentage for android layout?

UPDATE 2018:

PercentRelativeLayout and PercentFrameLayout are deprecated. Consider using ConstraintLayout

Old Answer:

So far Android Support library has limited on where to use this:

1. with RelativeLayout

   android.support.percent.PercentRelativeLayout
   

2. with FrameLayout

   android.support.percent.PercentFrameLayout
   

How to use it?

Well, first make sure to include the dependency at build.grade(Module: app) in your android app.

dependencies {
    compile 'com.android.support:percent:23.3.0'
}

Then navigate to your xml layout in this example (.MainActivity)

<android.support.percent.PercentRelativeLayout

  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:paddingBottom="@dimen/activity_vertical_margin"
  android:paddingLeft="@dimen/activity_horizontal_margin"
  android:paddingRight="@dimen/activity_horizontal_margin"
  android:paddingTop="@dimen/activity_vertical_margin"
  tools:context=".MainActivity">


  <Button
    android:id="@+id/button"
    android:text="Button"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    app:layout_widthPercent="30%"/>

  <Button    
    android:id="@+id/button2"
    android:text="Button 2"
    android:layout_height="wrap_content"
    android:layout_toRightOf="@id/button"
    app:layout_widthPercent="60%"/>

  <Button
    android:id="@+id/button3"
    android:text="Button 3"
    android:layout_height="wrap_content"
    android:layout_below="@+id/button"
    android:layout_alignParentStart="true"
    android:layout_alignParentLeft="true"
    app:layout_widthPercent="90%"/>

</android.support.percent.PercentRelativeLayout>

For more detail please check here:

You can use PercentRelativeLayout, It is a recent undocumented addition to the Design Support Library, enables the ability to specify not only elements relative to each other but also the total percentage of available space.

Structure Is

<android.support.percent.PercentRelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >
    <ImageView
        android:id="@+id/imageview"
        android:layout_gravity="center"
        app:layout_widthPercent="50%"
        app:layout_heightPercent="50%"
        android:src="@mipmap/ic_launcher"
        android:background="#cecece"/>
    <TextView
        android:id="@+id/textview1"
        android:layout_below="@id/imageview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_marginStartPercent="25%"
        app:layout_marginEndPercent="25%"
        android:text="PercentRelativeLayout example"
        android:background="#bebebe"/>


</android.support.percent.PercentRelativeLayout>

The Percent package provides APIs to support adding and managing percentage based dimensions in your app.

To use, you need to add this library to your Gradle dependency list:

dependencies {
    compile 'com.android.support:percent:22.2.0'
    // or compile 'com.android.support:percent:23.1.0'
}

For demo purpose you can visit Git android-percent-support-lib-sample.

The support library just added a percent layout.

It can be done like this

 <android.support.percent.PercentFrameLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent">
     <ImageView
         app:layout_widthPercent="50%"
         app:layout_heightPercent="50%"
         app:layout_marginTopPercent="25%"
         app:layout_marginLeftPercent="25%"/>
 </android.support.percent.PercentFrameLayout>

https://developer.android.com/reference/android/support/percent/PercentFrameLayout.html