/* How to calculate postgreSQL database size in disk ? */

SELECT pg_size_pretty(pg_database_size('thedbname'));

/* Calculate size of a table including or excluding the index */

SELECT pg_size_pretty(pg_total_relation_size('big_table'));
SELECT pg_size_pretty(pg_relation_size('big_table')); /* without index */

/* See indexes on a table with `\d tablename` */