Calculator Inputs
Example Data Table
| Example metric | Sample value | Why it matters |
|---|---|---|
| Named users | 1,200 | Total users define the starting population. |
| Simultaneous usage | 38% | Only a portion connects at the same time. |
| Average user bandwidth | 1.8 Mbps | Drives total throughput planning. |
| Protocol overhead | 18% | Adds encrypted tunnel and packet overhead. |
| CPU cost | 16 MHz per Mbps | Approximates encryption processing demand. |
| Server profile | 8 cores, 2.8 GHz, 32 GB RAM | Defines each node capacity. |
| Resilience target | 2 nodes minimum | Supports failover and maintenance windows. |
| Expected outcome | Multi-server cluster | Useful for production-grade secure access sizing. |
Formula Used
Base active sessions = Named users × Simultaneous usage %
Design sessions = Base active sessions × Peak factor × (1 + Growth reserve %)
Effective per-session throughput = Average user bandwidth × (1 + Protocol overhead %)
Total effective throughput = Design sessions × Effective per-session throughput
CPU required in GHz = Total effective throughput × CPU cost ÷ 1000
Tunnel memory = Design sessions × RAM per tunnel ÷ 1024
Servers by CPU, memory, and network are calculated independently. The final recommendation uses the highest count and respects the minimum resilience node count.
How to Use This Calculator
- Enter the total named user population.
- Estimate what percentage connects concurrently during busy periods.
- Enter realistic per-user bandwidth for your workload.
- Add peak factor and growth reserve to protect future capacity.
- Use measured or vendor-tested CPU cost per Mbps when possible.
- Enter your intended server hardware profile and safe utilization targets.
- Review the recommended server count and check the binding constraint.
- Use the chart to see how throughput, CPU, and memory scale.
FAQs
1. What does this VPN sizing calculator estimate?
It estimates design sessions, encrypted throughput, CPU demand, memory demand, per-server loading, logging volume, and recommended cluster size for a VPN deployment.
2. Why is simultaneous usage important?
Most user populations are not connected continuously. Simultaneous usage converts a total account count into a more realistic active-session estimate for sizing infrastructure.
3. What is protocol overhead?
Protocol overhead accounts for encapsulation, encryption headers, keepalives, and transport inefficiencies. It increases the actual bandwidth your servers and network interfaces must handle.
4. How should I choose CPU cost per Mbps?
Use benchmark data from your chosen cipher suite, VPN platform, packet size profile, and hardware generation. Measured values are always better than generic assumptions.
5. Why does the calculator recommend more than two servers?
Production VPN sizing is constrained by CPU, memory, or network. Even when redundancy needs only two nodes, one of those constraints may require a larger cluster.
6. Does this replace real load testing?
No. It is a planning model. You should still validate cipher choices, authentication flows, MTU behavior, packet loss, and user experience with a pilot or load test.
7. Can I use this for site-to-site tunnels?
Yes, but adjust session assumptions carefully. Site-to-site traffic usually has different concurrency, flow persistence, throughput patterns, and failover behavior than remote access VPN traffic.
8. What does binding constraint mean?
It shows whether CPU, memory, or network capacity forced the highest server count. That tells you which resource deserves the most attention during design refinement.