DB Growth Report with compression turned on???

Hi Everyone,I got into confusion while working on DB Growth report for 2012 databases which has compression on.I am analyzing the DB Growth based on MSDB..dbo.backupset table which stores the backup information.But here it gets tricky, In Previous versions we use "backup_size" column to get actual backup size and estimate the db growth based on the previous all backup file info. But now since compression is on in 2012 the "backup_size" colmuns gives a compressed file size(If i am right) so how do you know the actual backup size to estimate the db growth over a period of time??