# Monitoring your size flexible reservations for Amazon EC2
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Amazon EC2 Reserved Instances that apply to a Region provide Availability Zone flexibility and instance size flexibility. Reserved Instances that provide Availability Zone flexibility provide a discount on usage in any Availability Zone in the Region. Reserved Instances that provide instance size flexibility provide a discount on usage, regardless of instance size in that family. Size flexible Reserved Instances apply to the smallest instance sizes first. For more information, see [How Reserved Instances are applied](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/apply_ri.html) in the *Amazon EC2 User Guide*.

To understand how instance size flexibility provided by your Reserved Instance is applied to your usage, refer to the **lineItem/NormalizationFactor** and **lineItem/NormalizedUsageAmount** columns.

**Note**  
Instance size flexibility is supported only by Linux or Unix Reserved Instances with default tenancy that are assigned to a Region. For more information on the limitations of instance size flexibility for Regional Reserved Instances, see [How regional Reserved Instances are applied ](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/apply_ri.html#apply-regional-ri) in the *Amazon EC2 User Guide*.

In a Cost and Usage Report, the Reserved Instance usage is applied by default to the account that purchased the Reserved Instance. Any available Reserved Instance benefit that the purchasing account can’t use within the hour is then applied to other linked accounts based on the available matching On-Demand Instance usage.

## Example
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You purchase one `m4.xlarge` RI in a given Region. This `m4.xlarge` RI can be applied automatically to all `m4` instance usage in the same Region. In the following table, AWS applied the `m4.xlarge` to two separate `m4.large` instances.


|  |  |  |  | 
| --- |--- |--- |--- |
| lineItem/LineItemType | RIFee | Discounted Usage | Discounted Usage | 
| lineItem/ProductCode | AmazonEC2 | AmazonEC2 | AmazonEC2 | 
| lineItem/UsageStartDate | 2016-01-01T00:00:00Z | 2016-01-01T00:00:00Z | 2016-01-01T00:00:00Z | 
| lineItem/UsageType | HeavyUsage:m4.xlarge | BoxUsage:m4.large | BoxUsage:m4.large | 
| lineItem/LineItemDescription | USD 0.0618 hourly fee per Linux/UNIX (Amazon VPC), m4.xlarge instance | Linux/UNIX (Amazon VPC), m4.large Reserved Instance applied | Linux/UNIX (Amazon VPC), m4.large Reserved Instance applied | 
| lineItem/ResourceId |  | i-1bd250bc | i-1df340ed | 
| lineItem/UsageAmount |  | 1 | 1 | 
| lineItem/NormalizationFactor | 4 | 4 | 4 | 
| lineItem/NormalizedUsageAmount |  | 4 | 4 | 
| lineItem/UnblendedRate |  | 0 | 0 | 
| lineItem/UnblendedCost | 46 | 0 | 0 | 
| Reservation/ ReservationARN | arn:aws:ec2:us-east-1: 123456789012:reserved-instances /f8c204c1 | arn:aws:ec2:us-east-1: 123456789012:reserved-instances /f8c204c1 | arn:aws:ec2:us-east-1: 123456789012:reserved-instances /f8c204c1 | 
| Reservation/TotalReservedUnits | 744 |  |  | 
| Reservation/TotalReserved NormalizedUnits | 5952 |  |  | 

The two `m4.large` usage line items have different **ResourceId**s, and both received a discount benefit from the single `m4.xlarge` RI. This is shown by matching the **reservationARN** value across the usage and recurring monthly charge line items.

For more information about RI purchase options, see [How you are billed](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/concepts-reserved-instances-application.html#reserved-instances-payment-options) in the *Amazon EC2 User Guide*.