UDP Port Calculator
Calculate available UDP port range and usable ports after reserved and ephemeral ranges.
About UDP Port Calculator
UDP shares the same 16-bit port namespace as TCP (0–65535), with ports 0–1023 reserved as well-known ports requiring elevated privilege to bind on most systems, and this calculator lets you additionally exclude any organization-specific reserved ranges to find truly available ports for dynamic allocation. Each UDP socket also carries its own send/receive buffer allocation (controlled by SO_RCVBUF/SO_SNDBUF, defaulting from net.core.rmem_default/wmem_default), so total kernel memory committed to UDP scales with both port usage and per-socket buffer size.
Formula
Available UDP ports
available = 65535 − well_known(1024) − reserved
- R
- additional reserved/system ports
Worked example
With the default values below, UDP Port Calculator returns Available UDP Ports of 64,511. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Additional Reserved/System Portsaccepts 0–64,511
- 0
- Concurrent UDP Socketsminimum 1
- 200
- Per-Socket Buffer Size (KB)minimum 1
- 208
Results
- Available UDP Ports
- 64,511
- Total Buffer Memory Needed (MB)
- 40.63
- Available Ports per Concurrent Socket
- 322.6
Step by step
- 1Values used
- 2Available UDP ports
- 3Available UDP Ports= 64,511
- 4Total Buffer Memory Needed (MB)= 40.63
- 5Available Ports per Concurrent Socket= 322.6
Assumptions and limits
- The result is derived only from the 3 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
Do UDP and TCP ports share the same namespace?
No — despite both using 16-bit port numbers, UDP and TCP maintain independent port tables in the kernel, so binding UDP port 8080 does not conflict with a process listening on TCP port 8080. This calculator's range excludes well-known ports by convention, not because of a shared-namespace conflict.
How do I check the current UDP socket buffer defaults?
`sysctl net.core.rmem_default` and `sysctl net.core.wmem_default` show the default receive/send buffer sizes applied to new sockets that don't explicitly call setsockopt(SO_RCVBUF/SO_SNDBUF).
Why would I need a larger UDP buffer per socket?
Bursty UDP traffic (e.g. syslog floods, high-rate telemetry, VoIP/RTP streams) can overflow small receive buffers before the application reads them, causing silent packet drops — increasing SO_RCVBUF (up to net.core.rmem_max) gives the kernel more room to queue incoming datagrams during bursts.