Backing up to the cloud - do you have to B2D first?

I've only ever done back ups to tape drives before, but now that I'm investigating backing up to the cloud it looks like all other forms of backup require a backup to the disk first:

So presuming that is indeed the case, my next question is how much disk space should I expect a full backup to take? On this example server here's the disk capacity:

So would I expect the backup to take exactly 50.2GB or would it take more to allow for meta data etc?