Sometimes you gets alert for space issue on files system, and you see that there are too much space available in the datafiles.this script will help you to identify the limit , till which you can resize the data files.
Finding how much data files can be resize.

You can use below script to find out how much you can resize your datafiles.

SET VERIFY OFF
SET PAGES 60
COLUMN SMALLEST FORMAT 999,990
COLUMN CURRSIZE FORMAT 999,990
COLUMN SAVINGS FORMAT 999,990
COLUMN FILE_NAME FORMAT A50 WORD_WRAPPED
BREAK ON REPORT
COMPUTE SUM OF SAVINGS ON REPORT
COLUMN VALUE NEW_VAL BLKSIZE

SELECT FILE_NAME,
CEIL( (NVL(HWM,1)*&&BLKSIZE)/1024/1024 ) SMALLEST,
CEIL( BLOCKS*&&BLKSIZE/1024/1024) CURRSIZE,
CEIL( BLOCKS*&&BLKSIZE/1024/1024) - CEIL( (NVL(HWM,1)*&&BLKSIZE)/1024/1024 ) SAVINGS
FROM DBA_DATA_FILES DBADF, ( SELECT FILE_ID, MAX(BLOCK_ID+BLOCKS-1) HWM FROM DBA_EXTENTS GROUP BY FILE_ID ) DBAFS
WHERE DBADF.FILE_ID = DBAFS.FILE_ID(+);