How many On-Demand instances can I run in Amazon EC2?
There are five vCPU-based instance limits, each defines the amount of capacity you can use of a given instance family. All usage of instances in a given family, regardless of generation, size, or configuration variant (e.g. disk, processor type), will accrue towards the family’s total vCPU limit, listed in the table below. New AWS accounts may start with limits that are lower than the limits described here.