What units used in DBA_TABLESPACE_USAGE_METRICS? What units are used in the usage metrics (USED_SPACE and TABLESPACE_SIZE columns) described in Oracle's DBA_TABLESPACE_USAGE_METRICS static data dictionary view?

The Oracle Database Reference only tells they are the "Total space consumed by the tablespace" and "Total size of the tablespace", without mentioning units. Are they in bytes? Megabytes? Blocks?
Blocks. Blocks are the units of the DBA_TABLESPACE_USAGE_METRICS.USED_SPACE and DBA_TABLESPACE_USAGE_METRICS.TABLESPACE_SIZE. The latter column accounts for possible AUTOEXTEND MAXSIZE.

EDIT: I'm not sure what is the meaning of USED_SPACE for undo tablespace though. For example:

SQL&gt; SELECT tablespace_name, sum(blocks), status FROM dba_undo_extents GROUP BY tablespace_name, status ;

TABLESPACE_NAME                SUM(BLOCKS) STATUS
------------------------------ ----------- ---------
UNDOTBS1                               128 ACTIVE
UNDOTBS1                              5312 UNEXPIRED
UNDOTBS1                              8960 EXPIRED

SQL&gt; select USED_SPACE from DBA_TABLESPACE_USAGE_METRICS WHERE TABLESPACE_NAME='UNDOTBS1';

USED_SPACE
----------
      2864

SQL&gt; show parameter block_size

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_block_size                        integer     8192