Find the size of a table
In bytes:
select relpages * 8192 as size_in_bytes from pg_class where relname = 'mytable';
In human-readable form:
select pg_size_pretty(relpages * 8192) as size from pg_class where relname = 'mytable';
In bytes:
select relpages * 8192 as size_in_bytes from pg_class where relname = 'mytable';
In human-readable form:
select pg_size_pretty(relpages * 8192) as size from pg_class where relname = 'mytable';