Each event sent to an event hub counts as a billable message. An ingress event is defined as a unit of data that is less than or equal to 64 KB. Any event that is less than or equal to 64 KB in size is considered to be one billable event. If the event is greater than 64 KB, the number of billable events is calculated according to the event size, in multiples of 64 KB. For example, an 8-KB event sent to the event hub is billed as one event, but a 96-KB message sent to the event hub is billed as two events.
Events consumed from an event hub, and management operations and control calls such as checkpoints, aren't counted as billable ingress events, but accrue up to the throughput unit allowance.