Total user Database size in GB's

--- To fetch the User databases  Size in GBs use below query

SELECT    

DB_NAME(db.database_id) DatabaseName,    

(CAST(mfrows.RowSize AS FLOAT)*8)/1024/1024+(CAST(mflog.LogSize AS FLOAT)*8)/1024/1024 DBSizeGB

FROM sys.databases db    

LEFT JOIN (SELECT database_id,

                  SUM(size) RowSize

            FROM sys.master_files

            WHERE type = 0

            GROUP BY database_id, type) mfrows

    ON mfrows.database_id = db.database_id    

LEFT JOIN (SELECT database_id,

                  SUM(size) LogSize

            FROM sys.master_files

            WHERE type = 1

            GROUP BY database_id, type) mflog

    ON mflog.database_id = db.database_id    

        where db.database_id > 5

ORDER BY 1 DESC

---- Results are as below