The query above would now be written as:

SELECT pg_database.datname,
pg_shadow.usename AS owner,
pg_database_size(pg_database.datname) AS size,
pg_size_pretty(pg_database_size(pg_database.datname)) AS pretty_size
FROM pg_database
JOIN pg_shadow ON pg_database.datdba = pg_shadow.usesysid;

To get the size of a single table use:

SELECT pg_size_pretty( pg_total_relation_size(’my_table_name_here’) );