How to set numwidth in the grid output of PL/SQL developer?

Turns out this is possible!!!

Tools -> Preferences -> SQL Window -> Number fields to_char

You can also set the column format(Using the same table name as above...)

column reference_nr format 99999999999999999999999999999999

Select reference_nr from rss_ing_cc_imp;

REFERENCE_NR

      95209140353000001009592 
      25546980354901372045601 

Or ( new session ) which probably is better:

show numwidth

numwidth 10

Select reference_nr from rss_ing_cc_imp;

REFERENCE_NR

 9.5E+22 
 2.6E+22 

Set numwidth 30

show numwidth

numwidth 30

Select reference_nr from rss_ing_cc_imp;

REFERENCE_NR

   95209140353000001009592 
   25546980354901372045601

Use to_char, then you get the all the numbers:

select to_char ( t.reference_nr), t.reference_nr from rss_ing_cc_imp t
1   95209140353000001009592 9,5209140353E22
2   25546980354901372045601 2,55469803549014E22
3   75203220356000583867347 7,52032203560006E22
4   25546980357904327000017 2,55469803579043E22
5   95209140358000000700337 9,5209140358E22
6   95209140359000000596387 9,5209140359E22
7   25546980361131086003511 2,55469803611311E22
8   25546980361901390031808 2,55469803619014E22
9   85207130362051881964326 8,52071303620519E22
10  95209140363000000634885 9,5209140363E22
11  25546980364131099000436 2,55469803641311E22
12  95209141001000001006196 9,5209141001E22
13  85207131001100892094030 8,52071310011009E22
14  75203221001000590476576 7,52032210010006E22