We don't track the size of an individual log entry, much less provide a mechanism to tell you how much "a given blade" generates in terms of logs.
It's also a bit more complicated in that not do the logs themselves take up space, but the indexes do as well.
In addition to space for the logs and indexes, you also have packet captures from IPS and emulated files from Threat Emulation.
If you're using App Control and URL Filtering with Extended logging, you'll get all the URLs accessed by the user (if HTTPS Inspection is enabled), which obviously will take more space.