apt-get upgrade, strange download

when i give the command: apt-get upgrade
i get tekst that says it has to download 873MB of archives,
but after unpacking 165MB disc space will be used.
seems a bit strange to me.
is this OK, or is there something wrong?

[JohnnyH]

I should think that this means 165MB additional to the space already used by the packages that are being replaced by the upgrade.