avg - Piece size

 SET LINESIZE 200

COL avg_size_gb FOR 15

SELECT

    ROUND(AVG(size_gb), 2) AS avg_size_gb

FROM (

    SELECT

        ROUND(bp.bytes / 1024 / 1024 / 1024, 2) AS size_gb

    FROM

        v$backup_piece bp,

        v$backup_set bset

    WHERE

        bp.set_stamp = bset.set_stamp

        AND bp.set_count = bset.set_count

        AND bset.incremental_level IS NOT NULL

        AND bset.start_time > SYSDATE - 7

);