WCU: Write Capacity Units

DynamoDB requires the capacity to execute tasks related to writing. This capacity is called write capacity units (WCUs). In this lesson, we’re going to learn what they are, how to calculate them and dive into some considerations about them to be aware of when designing a system.

What is a WCU?

A write capacity unit (WCU) is the measurement unit used by DynamoDB to provide the resources that it will use to support writes to our table. The measurement unit is defined by record size and time. The first part is time, which corresponds to 1 second. The second part is the record size, which corresponds to a fixed size of 1 KB. That being said, we can state that a WCU is defined by the capacity of writing a 1 KB record to a table in 1 second.