Center multiple items in a RelativeLayout without putting them in a container?

android:gravity will align the content inside the view or layout it is used on.

android:layout_gravity will align the view or layout inside of his parent.

So adding

android:gravity="center"

to your RelativeLayout should do the trick…

Like this:

<RelativeLayout
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:layout_marginTop="15sp">

</RelativeLayout>