<resources>
    <dimen name="add_button_width">160dp</dimen>
    <dimen name="add_button_height">40dp</dimen>
</resources>

<Button
    android:id="@+id/btnAdd"
    android:layout_width="@dimen/add_button_width"
    android:layout_height="@dimen/add_button_height"
    android:text="Add"
   />