I have a PostgreSQL database, I made a backup copy of it and then I have installed the copy on another machine.

I noticed that the database size calculated with the query:

are significantly different on the two machines (the machine base is about twice the size).

I tried to make the VACUUM command but the dimensions have not changed.

What could be the cause of this difference?
There are other commands besides VACUUM to compact the database?

Thanks.

Are there any visible differences you may have missed with the two databases? Are the encoding both UTF8 on the original and the backup? Perhaps you didn't notice but your pg_restore didn't properly generate all the table data from the backup for some reason. Can you delete the backup from the server, VACUUM the database, pg_dump, move the dump to the new server & then pg_restore? Maybe something went wrong with out discovery.