SQL & PL/SQL

hello,

SELECT a.TABLESPACE_NAME,
a.BYTES bytes_used,
b.BYTES bytes_free,
b.largest,
ROUND(((a.BYTES-b.BYTES)/a.BYTES)*100,2) percent_used
FROM
(
SELECT TABLESPACE_NAME,
SUM(BYTES) BYTES
FROM dba_data_files
GROUP BY TABLESPACE_NAME
)
a,
(
SELECT TABLESPACE_NAME,
SUM(BYTES) BYTES ,
MAX(BYTES) largest
FROM dba_free_space
GROUP BY TABLESPACE_NAME
)
b
WHERE a.TABLESPACE_NAME=b.TABLESPACE_NAME
ORDER BY ((a.BYTES-b.BYTES)/a.BYTES) DESC;

i will insert this to a table...
--HOW DO I MAKE IT TO see in Gigabytes?