Background programatic drawable cropped

I want to make a button with a letter inside a circle, without using a picture.

My button is defined like this:

        <Button
            android:id="@+id/zoomInButton"
            android:layout_width="40dp"
            android:layout_height="40dp"
            android:layout_margin="10dp"
            android:background="@drawable/circle"
            android:text="+"
            android:textColor="@color/white"
            android:textSize="62sp" />

        <Button
            android:id="@+id/zoomOutButton"
            android:layout_width="40dp"
            android:layout_height="40dp"
            android:layout_margin="10dp"
            android:background="@drawable/circle"
            android:text="-"
            android:textColor="@color/white"
            android:textSize="62sp" />

And with circle being:

<stroke
    android:width="3dp"
    android:color="@color/white" />

<solid android:color="@android:color/transparent" />

However, the circle is not centred and the text is cropped:

How to center the background on the text?