If you don't have access to
There is a simple way:
test=# SELECT current_setting('block_size');
The following “parameters” are read-only, and are determined when
PostgreSQL is compiled or when it is installed. [...]
Reports the size of a disk block. It is determined by the value of
BLCKSZ when building the server. The default value is 8192 bytes. The
meaning of some configuration variables (such as shared_buffers) is
block_size. See Section 19.4 for information.
Create a dummy table with only 1 small row: one data page is allocated. Then check the size of the "main" relation fork with
test=# CREATE TEMP TABLE foo AS SELECT 1 AS id;
test=# SELECT pg_size_pretty(pg_relation_size('pg_temp.foo'));
So the page size is 8 kB, which is hardly surprising like you mentioned. The manual:
Every table and index is stored as an array of pages of a fixed size (usually 8 kB, although a different page size can be selected when compiling the server).