DynamoDB Item Size Calculator | RCU and WCU

DynamoDB item size calculator that sizes plain or DynamoDB JSON by AWS rules, shows RCU and WCU per read and write, and flags the 400 KB limit. Free.

Also known as: dynamodb item size calculator · dynamodb item size · dynamodb rcu wcu calculator · dynamodb capacity unit calculator · dynamodb item size limit · dynamodb 400kb limit · dynamodb consumed capacity calculator · dynamodb json size · dynamodb write capacity units calculator

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devops and infrastructure tools

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Item JSON

Input format

Size and Capacity

The item size in bytes, the read and write units it costs, and the attributes that make it heavy will appear here.

About DynamoDB Item Size Calculator

A DynamoDB item size calculator tells you how many bytes an item takes under DynamoDB's own sizing rules, which decide both the 400 KB item limit and how many read and write capacity units every request consumes. Paste an item as plain JSON or DynamoDB JSON and it sizes every attribute, then shows the RCU and WCU cost of each read and write.

Key Features

Sizes items with AWS's published rules: UTF-8 names and strings, raw binary bytes, and 3 bytes per list or map plus 1 per element
Numbers sized by digit pairs around the decimal point with all 38 digits kept; AWS documents number sizes as approximate
Reads plain JSON, DynamoDB JSON with S, N, B, SS, NS, BS, M, L, BOOL and NULL, or aws dynamodb get-item output
Read units for strongly consistent, eventually consistent and transactional reads, write units for standard and transactional writes
Ranks attributes by bytes so you can see which ones to shorten, compress or move to Amazon S3
Flags items over the 400 KB limit and numbers with more than 38 significant digits

Use Cases

Find out why a PutItem call fails with an item size error before it happens in production
Check whether an order record stays under 1 KB so every write costs a single WCU
See how much shortening attribute names like customerShippingAddress saves on a billion-item table
Estimate on-demand read and write costs for a new table in us-east-1
Decide when a growing list attribute should move to its own items or to S3
Explain consumed capacity numbers in CloudWatch to a teammate

Supported Formats

Plain JSON

DynamoDB JSON

aws dynamodb get-item output

.json files

Related Keywords

dynamodb item size calculator

dynamodb item size

dynamodb rcu wcu calculator

dynamodb capacity unit calculator

dynamodb item size limit

dynamodb 400kb limit

dynamodb consumed capacity calculator

dynamodb json size

dynamodb write capacity units calculator

How is a DynamoDB item's size calculated?

DynamoDB adds up the UTF-8 bytes of every attribute name and the size of every value. Strings count their UTF-8 bytes, binary values count their raw bytes rather than the base64 text, Booleans and nulls take 1 byte, and numbers take roughly 1 byte for every two significant digits plus 1. Lists and maps add 3 bytes of overhead plus 1 byte per element. Reads are rounded up to 4 KB per read unit and writes to 1 KB per write unit, so an item of 1,025 bytes costs two write units on every PutItem. Attribute names count toward all of this on every item, which is why short names matter on large tables.

Privacy & Security

All processing happens locally in your browser. Your data never leaves your computer, ensuring complete privacy and security.

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Frequently asked questions

What is DynamoDB Item Size Calculator used for?

DynamoDB item size calculator that sizes plain or DynamoDB JSON by AWS rules, shows RCU and WCU per read and write, and flags the 400 KB limit. Free.

Is DynamoDB Item Size Calculator free to use?

Yes. DynamoDB Item Size Calculator is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use DynamoDB Item Size Calculator?

No. DynamoDB Item Size Calculator works immediately in your browser with no signup, login, or email address required.

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