Getting the size of a DB

SELECT DB_NAME(database_id) AS DatabaseName,
Name AS Logical_Name,
Physical_Name, (size*8)/1024 SizeMB
FROM sys.master_files
WHERE DB_NAME(database_id) = 'NorthWind'
Ref : http://blog.sqlauthority.com/2010/02/08/sql-server-find-the-size-of-database-file-find-the-size-of-log-file/