What is the max item size in DynamoDB?

400 KB. The maximum item size in DynamoDB is 400 KB. That total counts both attribute names (UTF-8 byte length) and all attribute values (binary length), including nested lists and maps. Binary values are measured by raw byte length. There is no way to raise this limit — larger objects belong in Amazon S3.

What counts toward the 400 KB

The item size is the sum of:

• every attribute name, measured in UTF-8 bytes, and
• every attribute value, measured in binary length (strings as UTF-8, numbers compactly, binary as raw bytes).

Nested map and list structure adds a small per-element overhead too. Long attribute names cost real space — shorten them to save room.

Why it matters

Item size drives capacity cost: reads are metered per 4 KB and writes per 1 KB, rounded up. A larger item costs more per operation as well as risking the hard limit.

When you hit it

Split the data across multiple items, or move large blobs to Amazon S3 and store a reference in DynamoDB.

Go deeper

Measure any item with the item size calculator and read the item size limit guide. Download DynoTable to see item sizes as you edit.