Currently, each Provisioned IOPS volume in Amazon EBS can support up to 64,000 IOPS. Until you release the storage, EBS Provisioned IOPS SSD (io1) volumes are paid by the quantity you provision in GB per month. You'll be charged for Provisioned IOPS SSD (io1) volumes based on the quantity of IOPS (input/output operations per second) you provision multiplied by the percentage of days you provision for the month.
IOPS stands for input/output operations per second. The operations are measured in KiBs, and the underlying drive technology specifies the maximum amount of data that can be counted as a single I/O for each volume type.