Query database and table size

Command

SELECT relname AS table_name, pg_size_pretty(pg_total_relation_size(relid)) AS total_size, pg_size_pretty(pg_relation_size(relid)) AS data_only FROM pg_catalog.pg_statio_user_tables ORDER BY pg_total_relation_size(relid) DESC LIMIT 20;

What it does

Lists the 20 largest tables with their total size including indexes and TOAST.

When to use it

To analyze disk usage and find which tables take up space.

Caution

For the whole database size: SELECT pg_size_pretty(pg_database_size(current_database()));