Operations Manager 2012 Sizing Tool

The OpsMgr 2012 Sizing Helper is an interactive document designed to assist you with planning & sizing deployments of System Center 2012 Operations Manager. It helps you plan the correct amount of infrastructure needed for a new OpsMgr 2012 deployment, removing the uncertainties in making IT hardware purchases and optimizes cost. A typical recommendation will include minimum hardware specification for each server role, topology diagram and storage requirement.

https://blogs.technet.com/b/momteam/archive/2012/04/02/operations-manager-2012-sizing-helper-tool.aspx