How big are all the tables in the 'public' schema in postgres

total_disk_space.sql

WITH disk_tables AS
  (SELECT nspname,
          relname,
          pg_relation_size(c.oid) AS "size"
   FROM pg_class c
   LEFT JOIN pg_namespace n ON (n.oid = c.relnamespace)
   WHERE nspname IN ('public'))

SELECT pg_size_pretty(SUM(disk_tables.size)) FROM disk_tables;