The NetApp Fusion* tool is telling me ~65.02 TiB usable.
(*note: Fusion is for Partners and NetApp personal)
To manually calulate it you'll need to understand stand the way that ADP is configured on the disks.
Read more about root-data and root-data-data here: https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.dot-cm-concepts%2FGUID-B745CFA8-2C4C-47F1-A984-B95D3EBCAAB4.html
With this base config, you would end up with 4 total aggrs. 2 root aggrs and 2 data aggrs.
Each disk will have 3 total paritions. 1 root and 2 data. root partition is ~53.88 GiB each data parition is ~1.72 TiB.
