Connected to Oracle Database 18c Express Edition Release 18.0.0.0.0 
Connected as system@//192.168.1.201:1522/XE

SQL> 
SQL> SELECT
  2  ROUND(SUM (BYTES) / 1024 / 1024) "SIZE (MB)"
  3  FROM dba_extents;

 SIZE (MB)
----------
      2136

SQL> 
SQL> create table t(c varchar2(1000 char));

Table created


SQL> begin
  2  for c in 1..1e6 loop
  3    insert into t values(rpad('1', 1000, '0'));
  4  end loop;
  5  end;
  6  /

PL/SQL procedure successfully completed


SQL> 
SQL> SELECT
  2  ROUND(SUM (BYTES) / 1024 / 1024) "SIZE (MB)"
  3  FROM dba_extents;

 SIZE (MB)
----------
      3351


SQL> 



-- Create table
create table T
(
  c VARCHAR2(1000 CHAR)
)
tablespace SYSTEM
  pctfree 10
  pctused 40
  initrans 1
  maxtrans 255
  storage
  (
    initial 64K
    next 1M
    minextents 1
    maxextents unlimited
  );