DynamoDB Item sizes and formats - Amazon DynamoDB

DynamoDB Item sizes and formats

DynamoDB tables are schemaless, except for the primary key, so the items in a table can all have different attributes, sizes, and data types.

The total size of an item is the sum of the lengths of its attribute names and values, plus any applicable overhead as described below. You can use the following guidelines to estimate attribute sizes:

  • Strings are Unicode with UTF-8 binary encoding. The size of a string is (length of attribute name) + (number of UTF-8-encoded bytes).

  • Numbers are variable length, with up to 38 significant digits. Leading and trailing zeroes are trimmed. The size of a number is approximately (length of attribute name) + (1 byte per two significant digits) + (1 byte).

  • A binary value must be encoded in base64 format before it can be sent to DynamoDB, but the value's raw byte length is used for calculating size. The size of a binary attribute is (length of attribute name) + (number of raw bytes).

  • The size of a null attribute or a Boolean attribute is (length of attribute name) + (1 byte).

  • An attribute of type List or Map requires 3 bytes of overhead, regardless of its contents. The size of a List or Map is (length of attribute name) + sum (size of nested elements) + (3 bytes) . The size of an empty List or Map is (length of attribute name) + (3 bytes).

  • Each List or Map element also requires 1 byte of overhead.


We recommend that you choose shorter attribute names rather than long ones. This helps you reduce the amount of storage required, but also can lower the amount of RCU/WCUs you use.

For storage billing purposes, each item includes a per-item storage overhead that depends on the features you have enabled.

  • All items in DynamoDB require 100 bytes of storage overhead for indexing.

  • Some DynamoDB features (global tables, transactions, change data capture for Kinesis Data Streams with DynamoDB) require additional storage overhead to account for system-created attributes resulting from enabling those features. For example, global tables requires an additional 48 bytes of storage overhead.