Hello
It depends on the SP's included in the upgrade and also if you are using the upgrade drive for storing the downloaded files then you need to check the size of the downloaded file plus another 30 GB. Secondly you need to also make sure that the transport directory has enough free space.
I suggest you to read the upgrade guide:
https://websmp101.sap-ag.de/~sapidb/011000358700000749922010E
Here is what the upgrade guide says for EHP5:
Make sure that there is enough free disk space for the upgrade directory. This space is required for the upgrade and the logs and is distributed among several subdirectories.
For an estimation of the disk space needed for the upgrade directory, see Quick Guide [page 23]. The size may vary by up to 25%, depending on your database and source release.
Additionally read this SAP Note:
Note 186066 - Increased freespace requirement during the upgrade
Regards
RB