Why my EC2 instance have less RAM as instance type

When using commands such as free -h the total memory is what is available for usage to applications. It is not the total memory that the underlying virtual machine has been provisioned with. The difference exists as some part of that memory is used by the linux kernel. More details can be seen in this Ubuntu forum post: https://askubuntu.com/questions/743649/new-16gb-of-ram-installed-yet-i-see-15-3-on-my-system-why/743669#743669