Server array capacity calculator systems and methods are provided for estimating capacity based on diagnostic data. For example, a system comprising a database and an estimator computing device comprising a graphical user interface (GUI) and a capacity management module stored in memory and executed on a processor comprising instructions to receive diagnostic data from a plurality of servers of different server types, receive user input via the GUI, and in response to the user input, and for each of the server types, compute a current reference number of servers from current server efficiency estimates and a current number of utilized servers; calculate a growth multiplier from a ratio of the projected number of users and a count of the current concurrent users; generate a projected number of servers by multiplying the current reference number of servers with the growth multiplier, and display the projected number of servers on the GUI.