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NGINX Capacity Calculator

Derive NGINX connection capacity from worker processes and worker_connections, and the proxy buffer memory it commits.

About NGINX Capacity Calculator

Every connection slot in NGINX maps to a file descriptor, and a reverse-proxied request holds two — one facing the client and one facing the upstream. Little's law converts a request rate and duration into the number of slots actually occupied, which is usually a tiny fraction of the configured ceiling. Raising worker_connections without raising worker_rlimit_nofile is the classic NGINX misconfiguration, and the buffer memory column shows why a generous proxy_buffers setting can commit gigabytes of RAM.

Formula

NGINX Capacity

max connections = worker_processes × worker_connections; when proxying, each request consumes two slots (client and upstream), so proxied capacity is half that.

proxiedConnections
Half of max connections, because a proxied request holds two descriptors
concurrentRequests
Requests per second × duration, by Little's law

Worked example

With the default values below, NGINX Capacity Calculator returns Maximum Client Connections of 65,536. Change any input above and every figure here is recalculated in your browser.

Inputs used

worker_processesaccepts 1–512 workers
8 workers
worker_connectionsaccepts 64–1,000,000 connections
8,192 connections
Requests per secondaccepts 1–10,000,000 rps
30,000 rps
Average request durationaccepts 0.1–600,000 ms
25 ms
proxy_buffers per connectionaccepts 4–4,096 KB
32 KB

Results

Maximum Client Connections
65,536
Maximum Proxied Requests
32,768
Concurrent In-Flight Requests
750
Proxied Connection Utilisation
2.29%
Worst-Case Proxy Buffer Memory
2 GiB
File Descriptors Needed per Worker
16,416

Step by step

  1. 1Values used
  2. 2NGINX Capacity
  3. 3Maximum Client Connections= 65,536
  4. 4Maximum Proxied Requests= 32,768
  5. 5Concurrent In-Flight Requests= 750
  6. 6Proxied Connection Utilisation= 2.29
  7. 7Worst-Case Proxy Buffer Memory= 2,147,483,648
  8. 8File Descriptors Needed per Worker= 16,416

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 NGINX Capacity calculated?

max connections = worker_processes × worker_connections; when proxying, each request consumes two slots (client and upstream), so proxied capacity is half that. Every connection slot in NGINX maps to a file descriptor, and a reverse-proxied request holds two — one facing the client and one facing the upstream. Little's law converts a request rate and duration into the number of slots actually occupied, which is usually a tiny fraction of the configured ceiling.

Why does NGINX Capacity matter?

Raising worker_connections without raising worker_rlimit_nofile is the classic NGINX misconfiguration, and the buffer memory column shows why a generous proxy_buffers setting can commit gigabytes of RAM.

What values do I need to enter?

This calculator takes 5 inputs: worker_processes, worker_connections, Requests per second, Average request duration, proxy_buffers per connection. 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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