Sometimes its useful to know the space usage of individual database files. The following script uses the FILEPROPERTY function to display the space used by that file.
SELECT DB_NAME() AS DbName,
name AS FileName,
size/128.0 AS CurrentSizeMB,
size/128.0 - CAST(FILEPROPERTY(name, 'SpaceUsed') AS INT)/128.0 AS FreeSpaceMB
FROM sys.database_files;