Socket Buffer Calculator

Size per-socket send and receive buffers from the BDP, and total the kernel memory a server needs.

About Socket Buffer Calculator

A socket buffer has to hold one BDP of unacknowledged data, plus the kernel's own per-packet structures — which is why Linux treats the value in tcp_rmem as including roughly a 2× overhead. Multiplying by the connection count gives the memory the box must have spare. Buffers set too small throttle every transfer to window ÷ RTT; set too large across thousands of sockets they exhaust kernel memory and trigger connection resets under load.

Formulas

Socket Buffer

buffer = BDP × overhead factor, where BDP = bandwidth × RTT ÷ 8.

BDP: Bytes in flight for one socket
overhead factor: Linux charges roughly 2× the payload for skb bookkeeping

Server memory footprint

total kernel memory = per-socket buffer × concurrent sockets

concurrent sockets: Established connections held at peak

Worked example

With the default values below, Socket Buffer Calculator returns Buffer Per Socket of 4 MiB. Change any input above and every figure here is recalculated in your browser.

Inputs used

Bandwidth per socketminimum 0.1 Mbit/s: 200 Mbit/s
Round-trip timeminimum 0.1 ms: 80 ms
Concurrent socketsminimum 1 sockets: 500 sockets
Kernel overhead factoraccepts 1–4 ×: 2 ×

Results

Buffer Per Socket: 4 MiB
Bandwidth Delay Product: 2 MiB
Suggested tcp_rmem Max (power of two): 4 MiB
Total Buffer Memory: 2 GiB
Total Buffer Memory: 1,907.3 MB

Step by step

1Values used
2Socket Buffer
3Server memory footprint
4Buffer Per Socket= 4,000,000
5Bandwidth Delay Product= 2,000,000
6Suggested tcp_rmem Max (power of two)= 4,194,304
7Total Buffer Memory= 2,000,000,000
8Total Buffer Memory= 1,907.3 MB

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, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, 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 Socket Buffer calculated?

buffer = BDP × overhead factor, where BDP = bandwidth × RTT ÷ 8. A socket buffer has to hold one BDP of unacknowledged data, plus the kernel's own per-packet structures — which is why Linux treats the value in tcp_rmem as including roughly a 2× overhead. Multiplying by the connection count gives the memory the box must have spare.

Why does Socket Buffer matter?

Buffers set too small throttle every transfer to window ÷ RTT; set too large across thousands of sockets they exhaust kernel memory and trigger connection resets under load.

What values do I need to enter?

This calculator takes 4 inputs: Bandwidth per socket, Round-trip time, Concurrent sockets, Kernel overhead factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.