If you would like to know about the backup file compression on Sql Server 2008R2 and later version you can use the below scripts.
Note: Systems databases are not compressed for backup (master,model and msdb)
select
server_name,
database_name,
[type] AS Backup_type,
CAST(backup_size /1048576 AS DECIMAL (10,2)) AS [Backup_Size (MB)],
CAST(compressed_backup_size/1048576 AS DECIMAL (10,2)) AS [Compressed_Backup_Size (MB)],
100- ((compressed_backup_size/backup_size)*100) as "Compressed%",
backup_finish_date
from msdb.dbo.backupset
--where database_name ='db1' and [Type]='D'
order by backup_set_id desc
Note: Systems databases are not compressed for backup (master,model and msdb)
select
server_name,
database_name,
[type] AS Backup_type,
CAST(backup_size /1048576 AS DECIMAL (10,2)) AS [Backup_Size (MB)],
CAST(compressed_backup_size/1048576 AS DECIMAL (10,2)) AS [Compressed_Backup_Size (MB)],
100- ((compressed_backup_size/backup_size)*100) as "Compressed%",
backup_finish_date
from msdb.dbo.backupset
--where database_name ='db1' and [Type]='D'
order by backup_set_id desc