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WebSocket Capacity Calculator

Size WebSocket fan-out: servers required, message rate, bandwidth and the memory each long-lived connection pins.

About WebSocket Capacity Calculator

WebSocket connections are idle most of the time but never close, so capacity is driven by memory and file descriptors rather than request rate. The message rate and its bandwidth are computed separately because a large fan-out can be bandwidth-trivial and memory-enormous. Long-lived connections do not drain: after a deployment every client reconnects at once, so the per-server ceiling has to leave room for the whole population to land on the remaining nodes.

Formula

WebSocket Capacity

servers = ceil(connections ÷ per-server limit); message rate = connections × messages per minute ÷ 60; bandwidth = message rate × message size × 8.

perServer
Connections one server can hold, usually bounded by ephemeral ports and memory
memPerConnKb
Socket buffers plus application state per open connection

Worked example

With the default values below, WebSocket Capacity Calculator returns Servers Required of 4. Change any input above and every figure here is recalculated in your browser.

Inputs used

Concurrent WebSocket connectionsaccepts 1–100,000,000 connections
200,000 connections
Messages per connection per minuteaccepts 0–100,000 messages/min
6 messages/min
Average message sizeaccepts 1–10,000,000 bytes
512 bytes
Memory per connectionaccepts 1–8,192 KB
20 KB
Connections per serveraccepts 100–10,000,000 connections
60,000 connections

Results

Servers Required
4
Aggregate Message Rate
20,000 messages/s
Bandwidth
81.92 Mbps
Total Connection Memory
4 GiB
Memory per Server
977 MiB

Step by step

  1. 1Values used
  2. 2WebSocket Capacity
  3. 3Servers Required= 4
  4. 4Aggregate Message Rate= 20,000 messages/s
  5. 5Bandwidth= 81.92 Mbps
  6. 6Total Connection Memory= 4,096,000,000
  7. 7Memory per Server= 1,024,000,000

Assumptions and limits

  • The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency 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 WebSocket Capacity calculated?

servers = ceil(connections ÷ per-server limit); message rate = connections × messages per minute ÷ 60; bandwidth = message rate × message size × 8. WebSocket connections are idle most of the time but never close, so capacity is driven by memory and file descriptors rather than request rate. The message rate and its bandwidth are computed separately because a large fan-out can be bandwidth-trivial and memory-enormous.

Why does WebSocket Capacity matter?

Long-lived connections do not drain: after a deployment every client reconnects at once, so the per-server ceiling has to leave room for the whole population to land on the remaining nodes.

What values do I need to enter?

This calculator takes 5 inputs: Concurrent WebSocket connections, Messages per connection per minute, Average message size, Memory per connection, Connections per server. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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WebSocket Capacity Calculator – Calculate Servers Required