Stream Shard Count Calculator

Work out stream shard count instantly with clear inputs, formula shown and shareable results.

About Stream Shard Count Calculator

A stream shard has three independent limits: 1 MB/s and 1,000 records per second for writes, and 2 MB/s for reads shared across all consumers. Multiple consumer applications each read the full stream, so read throughput often binds first — three consumers on a 35 MB/s stream need enough shards for 105 MB/s of reads.

Formula

Shard count

write shards = ceil(MB/s / 1); record shards = ceil(records / 1000); read shards = ceil(MB/s x consumers / 2); shards = max of the three

Worked example

With the default values below, Stream Shard Count Calculator returns Shards required of 53. Change any input above and every figure here is recalculated in your browser.

Inputs used

Records per secondminimum 0.001: 12,000
Average record sizeminimum 0.001 KB: 3 KB
Consumer applications reading the streamminimum 1: 3
Retention periodaccepts 1–8,760 h: 24 h

Results

Shards required: 53
Write throughput: 35.16 MB/s
Binding constraint: Read throughput across consumers
Data retained in the stream: 2,966.3 GB

Step by step

1Values used
2Shard count
3Shards required= 53
4Write throughput= 35.16 MB/s
5Binding constraint= Read throughput across consumers
6Data retained in the stream= 2,966.3 GB

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the read limit avoided?

Enhanced fan-out gives each consumer its own dedicated 2 MB/s per shard, at extra cost per consumer-shard-hour. It also reduces propagation latency.

What causes a hot shard?

A partition key with low cardinality or heavy skew. Records with the same key always land on the same shard, so one popular key throttles that shard regardless of total capacity.