how to get postgresql page size?

Hi...

SELECT sum(relpages)* (PAGESIZE) FROM pg_class
WHERE relkind='r' AND relname = 'table'

I want to know how many disk space is a database table using something
like above

where (PAGESIZE) is the postgresql page size value.

how can I get the ??? value...

- I now default value for (PAGESIZE) is 8k, but if it was changed (BLCKSZ,
postgresql.h)?
- I need to know the (PAGESIZE) value without reading postgresql source
files...

-----------------------
Freddy Menjívar M.
ITCR

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