Estimate the size of the SQL file generated by pg_dump utility

Dear All,
I have to take backup of a database as a SQL file using the pg_dump
utility and I have to check the disk space
before taking the backup. Hence I need to estimate the size of the
pg_dump output.
The size given by pg_database_size procedure and the size of file
generated by pg_dump
vary to a large extent. Kindly let me know how to estimate the size of
the file that pg_dump generates.

Note: Please bear with us for the disclaimer because it is automated in
the exchange server.
Regards,
Ravi

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