How to estimate the size occupied by datafiles section in controlfile?

 Hi,       According to oracle documentation, the max control file is 20000 database blocks. The current blocks of our controlfile size is 10056 (with 8k as block size), which reaches half of the limit.  when querying v$controlfile_record_section using the sql below, the total size is less than 1M, which is way off from the actual controfil size ~82M. Where can I find the information of actual size distribution of controlfile?How do I estimate the size occupied by datafiles section in controlfile?
select sum(RECORD_SIZE/1024/1024) from  V$CONTROLFILE_RECORD_SECTION;


Thanks&Regards
Prem