Some of the most common questions we hear from users relate to capacity planning and hardware choices. How many replicas do I need? Should I consider sharding right away? How much RAM will I need for my working set? SSD or HDD? No one likes spending a lot of cash on hardware and cloud bills can just be as painful. MongoDB is different from traditional RDBMSs in its resource management, so you need to be mindful when deciding on the cluster layout and hardware. In this talk we will review the factors that drive the capacity requirements: volume of queries, access patterns, indexing, working set size, among others. Attendees will gain additional insight as we go through a few real-world scenarios, as experienced with MongoDB Inc customers, and come up with their ideal cluster layout and hardware.