How to use this calculator
- Enter peak concurrency for one primary site.
- Estimate what share of users remains active during failover.
- Choose how many primary failures to model.
- Add headroom and the number of backup sites still available.
#3126 · AI & Technology Tool
Network Redundancy Concurrent User Capacity Calculator
Estimate the concurrent-user capacity that standby infrastructure must absorb during a network failure. The calculator applies a failover share and headroom to primary concurrency, multiplies by the number of simultaneous primary failures, and distributes the requirement across available backup sites. It highlights the minimum whole-user capacity needed at each backup site.
Calculator
Failover users and standby sitesFormula
Expected failover users = primary users × failover share × simultaneous failures
Standby requirement = expected users × (1 + headroom)
Per backup site = ceil(standby requirement ÷ available backup sites)
Standby requirement = expected users × (1 + headroom)
Per backup site = ceil(standby requirement ÷ available backup sites)
What the result means
The main result is aggregate whole-user standby capacity. The per-site result rounds up so an even distribution does not under-provision any backup site.
This estimate assumes sessions can be redistributed evenly and that authentication, databases, licenses, and downstream services scale with the network edge.
Example calculation
At 1,200 peak users, 90% retained traffic, one primary failure, 20% headroom, and two backup sites, expected failover load is 1,080 users. Required standby capacity is 1,296 users, or 648 per backup site.
Tips for better results
- Use measured peak concurrency, not registered accounts.
- Test more than one failure if sites share a risk.
- Include reconnection surges in headroom.
- Verify session and license limits.
- Exercise the traffic-distribution policy regularly.
Frequently asked questions
Why can failover users be lower than primary peak users?
Some sessions may disconnect or be intentionally shed, which is represented by the retained-user percentage.
Why is per-backup capacity rounded up?
Rounding up prevents fractional allocation from leaving a backup site one user short.
Does the result include users already active on backup sites?
No. Add their existing peak load to the displayed per-site failover requirement.
Can I model two primary sites failing together?
Yes. Set simultaneous primary failures to two if each has the same entered peak concurrency.
What other limits should match user capacity?
Check compute, database connections, licenses, authentication throughput, and downstream bandwidth.
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Variables and units
| Variable | Meaning | Unit |
|---|---|---|
| U | Peak users per primary | users |
| f | Retained failover share | % |
| F | Simultaneous primary failures | sites |
| h | Standby headroom | % |