Declare
v_Rate Number(30,23);
v_suom    varchar2(20)  default 'BK';---runtime value pick
v_puom    varchar2(20)  default 'KG';--runtime value pick
v_itemid  number default  '12345';--runtime itemid pick
Begin
v_rate := inv_convert.inv_um_convert_new ( 
                           item_id                    => v_itemid
                          ,precision                 => NULL  
                          ,from_quantity      => 1             
                          ,from_unit               => v_suom
                          ,to_unit                     => v_puom
                          ,from_name            => NULL
                          ,to_name                  => NULL
                          ,capacity_type        => 'U'
                          );      

end;