Determining compression-factor 11g release 1

Working on 11g, release 1 (, managers wanted to know what kind of compression factor we achieved in the datawarehouse. Amount of (compressed) data: just about 1,5 TB. In all my naivity I thought Oracle delivered the package 'DBMS_COMPRESSION' which will show me the rate of achieved compression per table. But first of all, in 11gr1 there was no package like 'DBMS_COMPRESSION', this is only delivered with release 2.