Grid_Layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    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="org.technobyte.gridlayout.MainActivity">

    <GridLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true">

        <Button
            android:text="ADD +"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btnAdd"
            android:layout_column="0"
            android:layout_row="0" />

        <Button
            android:text="SUB -"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btnSub"
            android:layout_column="1"
            android:layout_row="0" />

        <Button
            android:text="MUL *"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btnMul"
            android:layout_column="3"
            android:layout_row="0"
            android:elevation="0dp" />

        <Button
            android:text="DIV /"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btnDiv"
            android:layout_column="4"
            android:layout_row="0" />

        <Button
            android:text="CALCULATE ="
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/btnCal"
            android:layout_column="0"
            android:layout_row="2"
            android:layout_columnWeight="0"
            android:layout_gravity="top|center"
            android:layout_columnSpan="5"
            android:minWidth="352dp" />

    </GridLayout>
</RelativeLayout>