How to list index subpartitions and their sizes

SELECT IDXSUBPART.INDEX_OWNER, IDXSUBPART.INDEX_NAME, IDXSUBPART.PARTITION_NAME, IDXSUBPART.SUBPARTITION_NAME,IDXSUBPART.TABLESPACE_NAME, ROUND(SUM(BYTES)/1024/1024/1024) "GB"
FROM   DBA_IND_SUBPARTITIONS IDXSUBPART JOIN DBA_SEGMENTS S
ON (IDXSUBPART.SUBPARTITION_NAME = S.PARTITION_NAME )
WHERE  IDXSUBPART.INDEX_NAME='SALES'
AND    IDXSUBPART.TABLESPACE_NAME='SH'
AND    S.SEGMENT_TYPE='INDEX SUBPARTITION'
GROUP BY IDXSUBPART.INDEX_OWNER, IDXSUBPART.INDEX_NAME, IDXSUBPART.PARTITION_NAME, IDXSUBPART.SUBPARTITION_NAME,IDXSUBPART.TABLESPACE_NAME;

Output:

INDEX_OWNER	INDEX_NAME	PARTITION_NAME	SUBPARTITION_NAME	TABLESPACE_NAME	GB
SH	SALES_IDX_SK1	SYS_P18153	SYS_SUBP14709	DATA1	1
SH	SALES_IDX_SK1	SYS_P18157	SYS_SUBP14831	DATA1	1
SH	SALES_IDX_SK1	SYS_P18158	SYS_SUBP14862	DATA2	25
SH	SALES_IDX_SK1	SYS_P18157	SYS_SUBP14832	DATA1	0
SH	SALES_IDX_SK1	SYS_P18142	SYS_SUBP12409	DATA2	32
SH	SALES_IDX_SK1	SYS_P18139	SYS_SUBP12414	DATA1	1