@dr If it's a managed table, you could get its size from TABLE_PARAMS table:
e.g.
SELECT a.TBL_NAME AS `TABLE`, b.PARAM_VALUE AS `SIZE` from TABLE_PARAMS b INNER JOIN TBLS a where a.TBL_ID=b.TBL_ID and b.PARAM_KEY='totalSize';
You could change the you need it. But, if there are external tables, or the table stats are not generated regularly, then you might not get the correct data.
You could get the table size using HDFS file system commands as well:
hdfs dfs -du -s -h <path to the table location>
This will give you more accurate data.