Finding the size of db and size of used space

Question

Greetings all good people.
Can you please help me find out about 2 database information?
One, I want to find out the size of a database =size of physical files.
and the size of data which is the size occupied in physical files.
We are about to start a new project and there is a table on the database but it is empty.
We want to be exporting data into this table but we want to make sure that there is enough space on the db before we start populating the table with data.
I believe the code below just gives me the size of the database.
select (bytes/1024/1024) as total_gigs from dba_segments where owner='BELL' and segment_name='$TABLE_NAME
But I want to know the total size of the database and how much size has been used already, much the same as you would want to know the size capacity of a hard drive and how much of the size has been used.
Sorry if my request is confusing.
Thanks a lot in advance

Answer 1

db size can be found out
select sum(bytes)/1024/1024/1024 from dba_data_files ;
and size of data is -- in the datafiles
select sum(bytes)/1024/1024/1024 from dba_segemnts ;
You can find out by below query .. the tablespace sizes -- would be DBSIZE
used space -- would be the actual occupied space.
select t.tablespace, t.totalspace as " Totalspace(MB)",
round((t.totalspace-nvl(fs.freespace,0)),2) as "Used Space(MB)",
nvl(fs.freespace,0) as "Freespace(MB)"
from
(select round(sum(d.bytes)/(1024*1024)) as totalspace,d.tablespace_name tablespace
from dba_data_files d
group by d.tablespace_name) t, (select round(sum(f.bytes)/(1024*1024)) as freespace,f.tablespace_name tablespace
from dba_free_space f
group by f.tablespace_name) fs
where t.tablespace=fs.tablespace (+)
order by t.tablespace