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"Capacity Planning" is a huge subject and it has many more aspects than just disk space (for example, memory, connections, connection speed, web servers, etc, etc ). To complicate matters, if it's a brand new system that you're standing up for brand new applications, then it requires some pretty deep esoteric knowledge of what the system does at the database level and what the expected number of transactions that will be stored over time and what those transactions will consist of. If it's an existing system, it's a little easier if the system has some history. For example, you can make some fairly decent estimates by plotting out the size of database backups. If you want something much more accurate, then you need to setup some code that measures the size of each database on a regular basis to develop some plot points so that you can calculate the growth trends for the future. An excellent introductory article on the subject with some embedded links on each part of capacity planning can be found at the following URL. Some of the links contain some code that you can instantiate to do some of the measurements over time that I speak of. [ https://sqlperformance.com/2016/11/sql-performance/capacity-planning-using-performance-data][1] Like I said and as stated in the article above, capacity planning is a huge subject and it's not just about disk space. There's way too much information to post here. You need to spend some serious time learning the art and that means spending some time doing research. I know people don't like to hear the ol' "Google It" answer but, unless you're willing to cough up some big bucks on shrink-wrapped tools to help (and they can be wrong) or expensive books on the subject or hire a consultant/consulting company , then Google is definitely your friend here. Please try the following search. [ https://sqlperformance.com/2016/11/sql-performance/capacity-planning-using-performance-data][2] Remember that capacity planning does take a good deal of knowledge and that it's a bit of an art rather than a pure science. For example, planning capacity based solely on history is a mistake. You also have to plan on expected new customers whether they're individuals hitting a web site like eBay or corporations that want to use a service such PLEX Systems. [1]: https://sqlperformance.com/2016/11/sql-performance/capacity-planning-using-performance-data [2]: https://sqlperformance.com/2016/11/sql-performance/capacity-planning-using-performance-data