Sizing SAP solutions can help you be more business oriented, and are proven to be cost effective. Sizing means determining the hardware requirements of an SAP system such as CPU power, physical memory, disk space and I/O, and network bandwidth. In order to calculate hardware requirements, customers can use the "Quick Sizer" a self-service tool available for free on the SAP Service Marketplace. Quick sizer has been available as a free self-service tool since 1996. It was developed in cooperation with SAP's hardware partners to help customers determine the parameters of their hardware needs. A short summary about the tool can be found here.
For sizing, SAP has identified three different and independent sizing models. The first two, user-based sizing and throughput-based sizing, have been implemented in the quick sizer as well:
On the SAP Service Marketplace, there's a wide range of documentation on how the quick sizer can be used. If you don't have access to the SAP Service Marketplace yet, follow www.service.sap.com/request-user. Besides quick sizer, SAP offers sizing guidelines and offline questionnaires for the SAP Business Suite application, SAP BusinessObjects portfolio solutions, SAP industry solutions, and SAP NetWeaver technology platform solutions. Which tools to use strongly depends on the size of the business, the complexity of the processes, and the resource consumption of the application.
Besides initial sizing, there is also productive sizing. Productive sizing means sizing for new functionalities or new users. There are different approaches for productive sizing, depending on the stage of a solution's lifecycle. Independent of the approach, you'll need to measure your current resource consumption (CPU utilization, table growth, and memory usage) in order to predict future resources. After having analyzed your system you add the extra load caused by additional users or new applications.
There's also decision support on the SAP Service Marketplace available, titled the "Sizing Decision Tree" . It provides you with the right information and helps you to find the right sizing strategy and therefore is very much adequate for colleagues who are not very familiar with sizing at SAP.
More information: Book: Sizing of SAP systems