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Connection Capacity Calculator

Find how many TCP connections a host can hold and whether memory, ports or the table is the limit.

About Connection Capacity Calculator

Three independent ceilings apply at once, and the smallest wins. Client-side sockets are usually port-bound because the local port range is shared, while server-side sockets are memory- or table-bound because they all land on one listening port. Knowing which ceiling binds tells you what to fix: adding RAM does nothing if you are out of ephemeral ports, and widening the port range does nothing if conntrack is full.

Formula

Connection Capacity

capacity = min(memory ÷ per-connection memory, ports × destinations, table limit).

ports × destinations
A 4-tuple is unique per destination, so each extra endpoint reuses the whole local port range
table limit
nf_conntrack_max or the application's own connection table

Worked example

With the default values below, Connection Capacity Calculator returns Usable Connection Capacity of 112,928. Change any input above and every figure here is recalculated in your browser.

Inputs used

Memory available for connectionsminimum 0.1 GB
16 GB
Memory per connectionminimum 1 KB
40 KB
Ephemeral port range sizeaccepts 1–65,535 ports
28,232 ports
Distinct destination endpointsminimum 1 endpoints
4 endpoints
Connection / conntrack table limitminimum 1 entries
262,144 entries

Results

Usable Connection Capacity
112,928 connections
Memory-Limited Capacity
419,430
Port-Limited Capacity
112,928
Binding Constraint
Ephemeral ports
Memory Used At Capacity
4.31 GB

Step by step

  1. 1Values used
  2. 2Connection Capacity
  3. 3Usable Connection Capacity= 112,928 connections
  4. 4Memory-Limited Capacity= 419,430
  5. 5Port-Limited Capacity= 112,928
  6. 6Binding Constraint= Ephemeral ports
  7. 7Memory Used At Capacity= 4.31 GB

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 Connection Capacity calculated?

capacity = min(memory ÷ per-connection memory, ports × destinations, table limit). Three independent ceilings apply at once, and the smallest wins. Client-side sockets are usually port-bound because the local port range is shared, while server-side sockets are memory- or table-bound because they all land on one listening port.

Why does Connection Capacity matter?

Knowing which ceiling binds tells you what to fix: adding RAM does nothing if you are out of ephemeral ports, and widening the port range does nothing if conntrack is full.

What values do I need to enter?

This calculator takes 5 inputs: Memory available for connections, Memory per connection, Ephemeral port range size, Distinct destination endpoints, Connection / conntrack table limit. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Why does the destination count multiply capacity?

A connection is identified by the full 4-tuple, so the same local port may be reused against a different destination IP or port. Fanning traffic across more backend endpoints multiplies the number of outbound connections a client can open.

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