Missed this one, but apparantly the Microsoft Exchange Team silently released a small update of the Exchange Mailbox Role Calculator, bringing it to version 14.4.

This version includes the following fixes since 14.2:

• Fixed stretched DAG scenario that had one database copy in each datacenter not reporting results due to new copy validation check
• Fixed secondary datacenter log disk calculations to correctly calculate the formatted disk space
• Fixed Table headers in the Storage Design tab to show disk count / Secondary datacenter
• Fixed two-node stretched DAG scenario that resulted in calculator not reporting results due to new copy validation check

You can download the calculator here, consult the changeblog here or read through the usage instructions here.