To get a list of the databases files, and the current disk size in MB, and the Free Space in MB in each fil, you can use this commands

USE [DATABASE_NAME]

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;

If you need a overview of all yours database this TSQL can be used

CREATE TABLE #FileSize
(dbName NVARCHAR(128), 
    FileName NVARCHAR(128), 
    type_desc NVARCHAR(128),
    CurrentSizeMB DECIMAL(10,2), 
    FreeSpaceMB DECIMAL(10,2)
);
    
INSERT INTO #FileSize(dbName, FileName, type_desc, CurrentSizeMB, FreeSpaceMB)
exec sp_msforeachdb 
'USE [?]; 
 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);';
    
SELECT * 
FROM #FileSize
WHERE dbName NOT IN ('distribution', 'master', 'model', 'msdb');
    
DROP TABLE #FileSize;