Socket Buffer Calculator
Calculate total kernel memory consumed by socket send and receive buffers system-wide.
About Socket Buffer Calculator
Every open TCP socket reserves separate receive (rmem) and send (wmem) buffer memory, and at scale — thousands of concurrent connections on a busy server — the aggregate memory committed to socket buffers alone can become a significant fraction of total system RAM, which is why per-socket buffer size and expected connection count both matter for capacity planning. The system-wide net.core.rmem_max (and wmem_max) sets a hard ceiling that per-socket auto-tuning or explicit setsockopt(SO_RCVBUF) calls cannot exceed, so a per-socket target above that ceiling is silently capped rather than honored.
Formula
Total socket buffer memory
total_memory = connections × (rmem + wmem)
- C
- concurrent connections
- rmem
- receive buffer per socket
- wmem
- send buffer per socket
Worked example
With the default values below, Socket Buffer Calculator returns Total Socket Buffer Memory (MB) of 494.79. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Concurrent Connectionsminimum 0
- 5,000
- Receive Buffer per Socket (bytes)minimum 1
- 87,380
- Send Buffer per Socket (bytes)minimum 1
- 16,384
- net.core.rmem_max (bytes)minimum 1
- 212,992
Results
- Total Socket Buffer Memory (MB)
- 494.79
- Memory per Connection (rmem + wmem, bytes)
- 103,764
- Per-Socket rmem Exceeds net.core.rmem_max?
- false
- rmem Headroom Below rmem_max (bytes)
- 125,612
Step by step
- 1Values used
- 2Total socket buffer memory
- 3Total Socket Buffer Memory (MB)= 494.79
- 4Memory per Connection (rmem + wmem, bytes)= 103,764
- 5Per-Socket rmem Exceeds net.core.rmem_max?= No
- 6rmem Headroom Below rmem_max (bytes)= 125,612
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 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 do I check current rmem/wmem defaults and maximums on Linux?
`sysctl net.ipv4.tcp_rmem net.ipv4.tcp_wmem` shows the three-value (min, default, max) auto-tuning ranges for TCP sockets; `sysctl net.core.rmem_max net.core.wmem_max` shows the hard system-wide ceilings that bound auto-tuning and explicit setsockopt calls alike.
Does every socket actually use its full configured buffer size?
No — Linux's TCP auto-tuning dynamically grows each socket's buffer between the configured min and max based on observed throughput and available memory, so idle or low-throughput connections typically use far less than the maximum, making this calculator's flat per-connection estimate a worst-case ceiling rather than typical usage.
What's the risk of setting rmem/wmem too high system-wide?
With very high concurrent connection counts, aggressively large per-socket buffers can exhaust system memory or trigger the kernel's memory pressure/OOM handling under load — buffer sizing should be based on actual bandwidth-delay product needs (see the Network Buffer Size Calculator) rather than maximized blindly.