Hello Alexandr,
other protocols don't send the full update every 30 seconds as RIP does so it is less important how many packets are needed to send out a full database.
OSPF uses different data structures named LSA.
Different types of LSAs exist so it is more difficult to say an OSPF LSU can carry X routes because it is dependent on the type of routes, type of LSAs that are inside the update packet.
And what is important each LSA is refreshed only once every 30 minutes and not every 30 seconds.
In normal conditions OSPF routers just exchange Hello packets every 10 seconds on Lan.
So we can say that bandwidth usage is lower for OSPF then RIP.
Then OSPF every 30 minutes require an LSA to be refreshed by its originator node.
To be noted that each LSA has its own age, sequence number and Advertising router-id and so they do not refresh all together.
I did some measurements and calculations some years ago but the bandwidth usage is rather low.
There was an old RFC about OSPF bandwidth usage.
see
http://tools.ietf.org/html/rfc1245
Hope to help
Giuseppe
