Following queries can be used for what you are looking for
Total indexed volume by index
|eventcount summarize=false report_size=true index=* | fields index count server size_bytes
Indexed volume for any period
index=_internal source=*metrics.log | eval MB=kb/1024 | timechart span=1h sum(MB) as TotalMB by series
Thanks. I dont know if it changed in one of the updates, but there used to be a screen (I think from the manager tab) that showed you all the information for total data indexed for your license.