How to check datafile usage in Oracle Database?

Below is the script script which will list datafile wise Allocated size, Used Size and Free Size
Size details are displayed in MB (Mega Bytes)

SELECT SUBSTR (df.NAME, 1, 40) file_name, df.bytes / 1024 / 1024 "Allocated Size(MB)",
((df.bytes / 1024 / 1024) - NVL (SUM (dfs.bytes) / 1024 / 1024, 0)) "Used Size (MB)",
NVL (SUM (dfs.bytes) / 1024 / 1024, 0) "Free Size(MB)"
FROM v$datafile df, dba_free_space dfs
WHERE df.file# = dfs.file_id(+)
GROUP BY dfs.file_id, df.NAME, df.file#, df.bytes
ORDER BY file_name;