There is a new page under the Control Panel that lets you calculate how much storage you use.
Note that Boomla uses a powerful storage engine that automatically detects when two files are identical and only stores them once, thereby reducing the storage space you use, thereby reducing your costs.
For example, taking snapshots of your websites, cloning them, or making a copy of an image won't use extra storage (except for a tiny metadata). We call this data deduplication as no duplicates are stored.
This is clearly a good idea. The only little downside is that this makes it harder to tell how much storage you actually use as simply adding up the size of all your files may give much larger results. Thus, you have to explicitly request calculating it. Hence the extra functionality.
Also, note that deleting a file or a website may have less of an impact on how much storage you use.
This calculation may take longer if you have large or many sites, so please be patient.