select ds.owner, sum(ds.bytes)/1024/1024/1024 as "Size in GB"
  from dba_segments ds
group by ds.owner
order by ds.owner;

SYS@XE_21.3.0.0.0> CREATE OR REPLACE FUNCTION get_total_clob_size
  2    (p_owner  IN VARCHAR2)
  3    RETURN	    NUMBER
  4  AS
  5    v_size	    NUMBER := 0;
  6    v_total_size NUMBER := 0;
  7    e_not_exist  EXCEPTION;
  8    e_no_privs   EXCEPTION;
  9    PRAGMA EXCEPTION_INIT (e_not_exist, -00942);
 10    PRAGMA EXCEPTION_INIT (e_no_privs,  -01031);
 11  BEGIN
 12    FOR i IN
 13  	 (SELECT column_name, owner, table_name
 14  	  FROM	 dba_tab_columns
 15  	  WHERE  UPPER (owner) = UPPER (p_owner)
 16  	  AND	 data_type = 'CLOB'
 17  	  AND	 owner NOT IN ('SYS', 'SYSTEM')
 18  	  -- AND any other criteria you can use to limit it to xml or pdf
 19  	 )
 20    LOOP
 21  	 BEGIN
 22  	   EXECUTE IMMEDIATE
 23  	     'SELECT SUM(DBMS_LOB.GETLENGTH("' || i.column_name || '"))/1024/1024/1024
 24  	      FROM   "' || i.owner || '"."' || i.table_name || '"'
 25  	     INTO v_size;
 26  	 EXCEPTION
 27  	   WHEN e_not_exist THEN v_size := 0;
 28  	     DBMS_OUTPUT.PUT_LINE (i.owner || '.' || i.table_name || ' does not exist');
 29  	   WHEN e_no_privs THEN v_size := 0;
 30  	     DBMS_OUTPUT.PUT_LINE (i.owner || '.' || i.table_name || ' fsinsufficient privileges');
 31  	 END;
 32  	 v_total_size := v_total_size + NVL(v_size,0);
 33    END LOOP;
 34    RETURN v_total_size;
 35  END get_total_clob_size;
 36  /

Function created.

SYS@XE_21.3.0.0.0> SHOW ERRORS
No errors.
SYS@XE_21.3.0.0.0> column owner format a30
SYS@XE_21.3.0.0.0> select t1.owner, t1."Size in GB", nvl (t2."Clobs in GB", 0) as "Clobs in GB",
  2  	    t1."Size in GB" - nvl (t2."Clobs in GB", 0) as "without clobs"
  3  from   (select ds.owner,
  4  		    sum(ds.bytes)/1024/1024/1024 as "Size in GB"
  5  	     from   dba_segments ds
  6  	     group  by ds.owner) t1,
  7  	    (select owner, get_total_clob_size (owner) as "Clobs in GB"
  8  	     from   (select distinct owner
  9  		     from   dba_tab_columns
 10  		     where  data_type = 'CLOB')) t2
 11  where  t1.owner = t2.owner(+)
 12  order  by t1.owner
 13  /

OWNER                          Size in GB Clobs in GB without clobs             
------------------------------ ---------- ----------- -------------             
AUDSYS                         .028381348  .000062657    .028318691             
C##SCOTT                       .082275391  .000011489    .082263902             
CTXSYS                         .002990723           0    .002990723             
DBSNMP                         .000183105           0    .000183105             
DVSYS                          .004455566           0    .004455566             
GSMADMIN_INTERNAL              .001098633           0    .001098633             
LBACSYS                        .000305176           0    .000305176             
MDSYS                          .167236328  .030518234    .136718094             
OJVMSYS                        .000366211           0    .000366211             
ORDDATA                        .001281738           0    .001281738             
ORDSYS                         .000366211           0    .000366211             
OUTLN                          .000549316           0    .000549316             
SYS                            1.75708008           0    1.75708008             
SYSTEM                         .018310547           0    .018310547             
WMSYS                          .007141113           0    .007141113             
XDB                            .099609375           0    .099609375             

16 rows selected.

SQL> select owner, sum(bytes)/1024/1024/1024 as "Size in GB"
  2  from dba_segments
  3  where (owner,segment_name) not in
  4        (select owner, segment_name from dba_lobs)
  5  group by owner
  6  order by owner
  7  /
OWNER                          Size in GB
------------------------------ ----------
APEX_030200                    .071166992
APPQOSSYS                       .00012207
CTXSYS                         .003723145
DBSNMP                         .000549316
DMUSER                         .009216309
EXFSYS                         .003662109
FIXXXER                        .000244141
HR                             .001525879
IX                             .001525879
MC_RMAN                        .000915527
MDSYS                          .022705078
MICHEL                         5.70141602
MICHEL2                        .000061035
OE                             .007873535
OLAPSYS                        .008605957
OPS$MICHEL                     .000366211
ORDDATA                        .010498047
ORDSYS                         .000427246
OUTLN                          .000488281
PERFSTAT                       .108154297
PM                             .001464844
SCOTT                          .002197266
SH                             .180603027
SYS                            1.25653076
SYSMAN                         .049682617
SYSTEM                          .08001709
TEST                           .000244141
WATCHER                        .000427246
WMSYS                          .002929688
XDB                            .047485352