SELECT 
    df.tablespace_name AS "Tablespace",
    totalusedspace AS "Used MB",
    (df.totalspace - tu.totalusedspace) AS "Free MB",
    df.totalspace AS "Total MB",
    ROUND(100 * ( (df.totalspace - tu.totalusedspace) / df.totalspace)) AS "% Free"
FROM
    (SELECT 
        tablespace_name,
        ROUND(SUM(bytes) / 1048576) TotalSpace
    FROM 
        dba_data_files
    GROUP BY 
        tablespace_name) df,
    (SELECT 
        ROUND(SUM(bytes)/(1024*1024)) totalusedspace,
        tablespace_name
    FROM 
        dba_segments
    GROUP BY 
        tablespace_name) tu
WHERE 
    df.tablespace_name = tu.tablespace_name;