DynamoDB Read/Write Capacity and On-Demand Mode

DynamoDB's pricing and performance are governed by capacity modes. Understanding the difference between provisioned and on-demand capacity — and when to use each — is essential for controlling costs and avoiding throttling.

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Capacity Units Explained

DynamoDB measures throughput in Read Capacity Units (RCUs) and Write Capacity Units (WCUs).

Read Capacity Units (RCU)

Read Type	Item Size	RCUs Consumed
Strongly consistent	≤ 4 KB	1 RCU
Eventually consistent	≤ 4 KB	0.5 RCU
Transactional	≤ 4 KB	2 RCUs

For items larger than 4 KB, DynamoDB rounds up to the next 4 KB boundary. A 6 KB strongly consistent read consumes 2 RCUs (rounded to 8 KB ÷ 4 KB = 2).

Write Capacity Units (WCU)

Write Type	Item Size	WCUs Consumed
Standard	≤ 1 KB	1 WCU
Transactional	≤ 1 KB	2 WCUs

A 2.5 KB write consumes 3 WCUs (rounded up to 3 KB).

Calculation Examples