This question already has an answer here:
Despite my colleague and myself being application developers by nature, our current contract engagement has placed us into the infrastructure operations branch of our customer. While we are still largely responsible for the framework and architecture levels of .NET code base, we are also involved in capacity planning – reviewing the requirements and volume from proposed projects, the general solution/approach, and map them to the existing infrastructure and network topology. There we have to calculate which existing resources can handle the load, where new servers and bandwidth need to be allocated, etc. These projects apply to a great area of their systems and topology.
The thing is: the customer themselves do not have a standard practice. There is no set methodology to evaluate these, no template documents to document and calculate these figures in a consistent manner. How they managed all the past developments of such scale is a mystery presently. I would like to ask if there are any capacity planning guides and advice we can refer to point us in the right direction towards more accurate calculations?