Example:

Free space for the file in the below query result set will be returned by the FreeSpaceMB column.

SELECT DB_NAME() AS DbName,

name AS FileName,

type_desc,

size/128.0 AS CurrentSizeMB,

size/128.0 - CAST(FILEPROPERTY(name, 'SpaceUsed') AS INT)/128.0 AS FreeSpaceMB

FROM sys.database_files

WHERE type IN (0,1);