How to use this calculator
- Enter the smaller usable upload or download rate.
- Reserve capacity for data traffic and bursts.
- Enter codec bitrate and packet overhead.
- Add a signaling allowance and calculate the whole-call capacity.
#3106 · AI & Technology Tool
VoIP System Concurrent User Capacity Calculator
Estimate how many simultaneous VoIP calls a link can carry after protecting part of the circuit for other traffic and accounting for on-the-wire overhead. This planning tool converts codec payload bitrate into bandwidth per call, applies signaling allowance, and rounds capacity down to a whole call. It is best used on the slower of the upload and download paths.
Calculator
Planning inputsFormula
Voice-usable kbps = Mbps × 1,000 × (1 − reserve). Per-call kbps = codec × (1 + overhead) × (1 + signaling). Capacity = floor(usable ÷ per call).
What the result means
The result is the maximum whole-call count allowed by the entered bandwidth assumptions. Other system limits may be lower.
Use the bottleneck direction. A circuit advertised as asymmetric may support fewer calls upstream even when downstream capacity is ample.
Example calculation
A 20 Mbps bottleneck with 30% reserved leaves 14 Mbps for voice. At 64 kbps, 35% packet overhead, and 5% signaling, each call needs 90.72 kbps, giving 154 concurrent calls.
Tips for better results
- Base capacity on the slower network direction.
- Use measured packet overhead for your exact tunnel and codec.
- Leave room for call bursts and failover.
- Compare against SBC and license session limits.
- Validate busy-hour packet loss after deployment.
Frequently asked questions
Why does this use the limiting network direction?
A bidirectional call fails if either upload or download is constrained, so capacity should use the smaller available direction.
Why is the answer rounded down?
Each active call needs its full provisioned rate. The unused fraction cannot safely carry another whole call.
Does this include call signaling?
Yes, the entered signaling allowance increases the per-call planning rate, although real signaling is often bursty.
Can codec compression increase capacity?
A lower codec payload rate can increase bandwidth capacity, but quality, packet overhead, CPU use, and transcoding requirements must also be considered.
Is this the same as licensed session capacity?
No. Licenses, trunks, SBCs, gateways, and call-platform limits can cap sessions below the network bandwidth result.
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Capacity calculation terms
| Term | Definition |
|---|---|
| Limiting direction | Lower of usable upload and download |
| Voice reserve | Share remaining after other traffic is protected |
| Per-call rate | Codec plus packet and signaling allowances |
| Whole-call capacity | Usable rate divided by per-call rate, rounded down |