What does AWS RI Instance Size Flexibility mean and how does it work?

Can I upsize or downsize within the same instance family, is there a price reduction in the monthly AWS bill?

Some AWS Standard RIs for RDS & EC2 offer instance size flexibility meaning that regardless of the RI size you have, it can cover running instances of any size in its particular family.

This means that if you scale up an instance, the smaller contract sizes will accumulate to cover the machine, as long as the total hours being used are less than what is reserved. You can easily verify this on your invoice and observe it reflected on our billing savings page.

AWS offers more detailed information regarding Instance Size Flexibility for EC2 Reserved Instances and certain RDS instances, including details about the instance sizes and their associated normalization factors.