OpenVPN Performance Calculator
Estimate OpenVPN tunnel throughput and MTU from cipher choice, transport protocol and instance count.
Inputs
Expected Throughput
949.6Mbps
Cipher Ceiling
1,040.0Mbps
Tunnel MTU
1,431bytes
Protocol Overhead
5.04%
Bottleneck
Circuit bandwidth
Step by step
Values used
Link rate = 1,000 Mbps; Cipher and CPU support = AES-256-GCM with AES-NI (520 Mbps/instance); Transport and overhead = UDP tun mode (69 B); Average packet size = 1,300 bytes; Path MTU = 1,500 bytes; Parallel OpenVPN instances = 2 instances
OpenVPN Performance
throughput = min(link rate × payload ÷ (payload + overhead), cipher rate × instances), with overhead 69 B for UDP and 89 B for TCP.
Expected Throughput
= 949.6 Mbps
Cipher Ceiling
= 1,040.0 Mbps
Tunnel MTU
= 1,431 bytes
Protocol Overhead
= 5.04
Bottleneck
= Circuit bandwidth
How it works
OpenVPN's data channel is single-threaded, so one process is capped by cipher speed no matter how many cores exist; scaling comes from running several instances behind a load balancer. The wire cost is 69 bytes over UDP and 89 over TCP once the extra TCP header and length prefix are counted. It explains the classic complaint that a 1 Gbps circuit only delivers 300 Mbps over OpenVPN, and shows whether the fix is AES-NI, GCM or more daemons.
Formula
OpenVPN Performance
throughput = min(link rate × payload ÷ (payload + overhead), cipher rate × instances), with overhead 69 B for UDP and 89 B for TCP.
- cipher rate
- Data-channel throughput one OpenVPN process sustains on this CPU
- instances
- Independent daemons or --multihome workers sharing the load
Frequently Asked Questions
How is OpenVPN Performance calculated?
throughput = min(link rate × payload ÷ (payload + overhead), cipher rate × instances), with overhead 69 B for UDP and 89 B for TCP. OpenVPN's data channel is single-threaded, so one process is capped by cipher speed no matter how many cores exist; scaling comes from running several instances behind a load balancer. The wire cost is 69 bytes over UDP and 89 over TCP once the extra TCP header and length prefix are counted.
Why does OpenVPN Performance matter?
It explains the classic complaint that a 1 Gbps circuit only delivers 300 Mbps over OpenVPN, and shows whether the fix is AES-NI, GCM or more daemons.
What values do I need to enter?
This calculator takes 6 inputs: Link rate, Cipher and CPU support, Transport and overhead, Average packet size, Path MTU, Parallel OpenVPN instances. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.