Socket Buffer Calculator

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

Inputs

Bandwidth per socketMbit/s

Round-trip timems

Concurrent socketssockets

Kernel overhead factor×

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

1,907.3MB

Step by step

Values used
Bandwidth per socket = 200 Mbit/s; Round-trip time = 80 ms; Concurrent sockets = 500 sockets; Kernel overhead factor = 2 ×
Socket Buffer
buffer = BDP × overhead factor, where BDP = bandwidth × RTT ÷ 8.
Server memory footprint
total kernel memory = per-socket buffer × concurrent sockets
Buffer Per Socket
= 4,000,000
Bandwidth Delay Product
= 2,000,000
Suggested tcp_rmem Max (power of two)
= 4,194,304
Total Buffer Memory
= 2,000,000,000
Total Buffer Memory
= 1,907.3 MB

How it works

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

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.

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