Yet another way to get exactly what was originally asked for is to use gs.sql(), if you're on Fuji or older release (it no longer works from Geneva):

gs.sql("SELECT CONCAT('YOUR INSTANCE DATABASE IS CURRENTLY ', ROUND(SUM(data_length + index_length) / 1024 / 1024 / 1024, 1), ' GB') DB_SIZE_GB FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE='BASE TABLE'");

gives (based on table sizes; took 180 ms)

DB_SIZE_GB

YOUR INSTANCE DATABASE IS CURRENTLY 2.8 GB

To get the size per table for all tables, with the largest first, use

gs.sql("SELECT TABLE_NAME, TABLE_ROWS, ROUND(((data_length + index_length) / 1024 / 1024), 2) TABLE_SIZE_MB FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE='BASE TABLE' ORDER BY 3 DESC");

gives (took 308 ms)

TABLE_NAME, TABLE_ROWS, TABLE_SIZE_MB

sys_upgrade_history_log, 340131, 1458.94

sys_attachment_doc, 20109, 220.16

sys_user_token, 149572, 82.78

sys_audit, 55394, 61.13

syslog_transaction0006, 72771, 59.75

syslog_transaction0002, 65791, 56.73

syslog_transaction0003, 68679, 56.73

syslog_transaction0004, 57225, 55.67

sys_metadata, 72777, 53.97

syslog_transaction0005, 58621, 51.81

usageanalytics_count, 35119, 40.75

syslog_transaction0001, 42843, 38.75

syslog_transaction0007, 34261, 31.80

...

To use gs.sql(), you have to elevate privilege to security_admin and use "Scripts - Background" from the Navigator.

WARNING: misuse of gs.sql() may cause unrecoverable damage to your instance.

Please feel free to connect, follow, mark helpful / answer, like, endorse.

John Chun, PhD PMP