Floating ActionButton

<?xml version="1.0" encoding="utf-8"?> 
<androidx.constraintlayout.widget.ConstraintLayout
	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"
	tools:context=".MainActivity"
	tools:ignore="HardcodedText"> 

	<!-- This will be the parent Floating Action Button -->
	<!-- After the implementation the Floating Action Button 
		at the bottom right corner -->
	<!-- After clicking the above button the following two buttons 
		will pop up. So this button is considered as parent FAB -->
	<com.google.android.material.floatingactionbutton.FloatingActionButton
		android:id="@+id/add_fab"
		android:layout_width="wrap_content"
		android:layout_height="wrap_content"
		android:layout_gravity="end"
		android:layout_marginEnd="16dp"
		android:layout_marginBottom="16dp"
		android:src="@drawable/ic_add_black_24dp"
		app:fabSize="normal"
		app:layout_constraintBottom_toBottomOf="parent"
		app:layout_constraintEnd_toEndOf="parent" /> 

	<!-- Floating action button for add alarm -->
	<!-- Make sure that you are constraining this 
		button to the parent button -->
	<com.google.android.material.floatingactionbutton.FloatingActionButton
		android:id="@+id/add_alarm_fab"
		android:layout_width="wrap_content"
		android:layout_height="wrap_content"
		android:layout_marginBottom="24dp"
		app:fabSize="normal"
		app:layout_constraintBottom_toTopOf="@+id/add_fab"
		app:layout_constraintEnd_toEndOf="@+id/add_fab"
		app:layout_constraintStart_toStartOf="@+id/add_fab"
		app:srcCompat="@drawable/ic_add_alarm_black_24dp" /> 

	<!-- Action name text for the add alarm button -->
	<!-- Make sure that you are constraining this Text to 
		the add Alarm FAB button -->
	<TextView
		android:id="@+id/add_alarm_action_text"
		android:layout_width="wrap_content"
		android:layout_height="wrap_content"
		android:layout_marginEnd="8dp"
		android:text="Add Alarm"
		app:layout_constraintBottom_toBottomOf="@+id/add_alarm_fab"
		app:layout_constraintEnd_toStartOf="@+id/add_alarm_fab"
		app:layout_constraintTop_toTopOf="@+id/add_alarm_fab" /> 

	<!-- Floating action button for add person -->
	<!-- Make sure that you are constraining this 
		button to the add Alarm FAB button -->
	<com.google.android.material.floatingactionbutton.FloatingActionButton
		android:id="@+id/add_person_fab"
		android:layout_width="wrap_content"
		android:layout_height="wrap_content"
		android:layout_marginBottom="24dp"
		app:fabSize="normal"
		app:layout_constraintBottom_toTopOf="@+id/add_alarm_fab"
		app:layout_constraintEnd_toEndOf="@+id/add_alarm_fab"
		app:layout_constraintStart_toStartOf="@+id/add_alarm_fab"
		app:srcCompat="@drawable/ic_person_add_black_24dp" /> 

	<!-- Action name text for the add person button -->
	<!-- Make sure that you are constraining this Text 
		to the add Person FAB button -->
	<TextView
		android:id="@+id/add_person_action_text"
		android:layout_width="wrap_content"
		android:layout_height="wrap_content"
		android:layout_marginEnd="8dp"
		android:text="Add Person"
		app:layout_constraintBottom_toBottomOf="@+id/add_person_fab"
		app:layout_constraintEnd_toStartOf="@+id/add_person_fab"
		app:layout_constraintTop_toTopOf="@+id/add_person_fab" /> 
</androidx.constraintlayout.widget.ConstraintLayout>

• answer : app:fabCustomSize="40dp" set size according your need

• fab default size 56dp X 56dp