Check the size of databases in SQL Server

SELECT DB_NAME(database_id) AS DatabaseName,
 size * 8 / 1024 AS SizeMB
FROM sys.master_files

Check the data file size in SQL Server

SELECT DB_NAME(database_id) AS DatabaseName,physical_name,
 size * 8 / 1024 AS SizeMB
FROM sys.master_files

Monitor the disk space in SQL Server

EXEC xp_fixeddrives;