Estimate how many simultaneous VoIP calls a fixed network bandwidth allocation can support. The calculator divides the usable share of available Mbps by an on-wire per-call bitrate, then rounds down to a whole number because a partial call cannot be supported as a capacity unit.
It is useful when an existing WAN, VPN, or site link has a known voice allocation and you need a quick concurrency estimate. The result depends on the per-call bitrate being realistic for the codec, packetization interval, and encapsulation in use. It is a bandwidth capacity estimate only; call-server licensing, SIP trunk limits, CPU capacity, and QoS policy can impose separate limits.
1. Enter allocated bandwidth
Use the part of the link reserved or safely available for voice traffic.
2. Enter per-call bitrate
Use a network bitrate that includes codec and protocol overhead.
3. Set usable allocation
Reserve some of the voice allocation for variability rather than planning to 100%.
4. Review call capacity
The result rounds down to the maximum whole-number concurrent calls that fit.
The calculation assumes each active call consumes approximately the same network bitrate.
The result is the bandwidth-limited number of simultaneous calls supported under the entered assumptions.
The practical system limit is the lowest of bandwidth capacity, trunk capacity, licenses, session-border-controller limits, and platform capacity.
Given: 20 Mbps allocated to VoIP, 100 kbps per call, and 80% usable allocation.
Calculation: Usable capacity = 20 × 1,000 × 0.80 = 16,000 kbps. Calls = floor(16,000 ÷ 100) = 160.
Result: About 160 concurrent calls based on bandwidth.
Capacity planning must fit every complete call within the usable bandwidth. Rounding up could imply supporting a call that does not fully fit.
Yes. Different codecs and packetization settings can have different on-wire bitrates, so the same link can support different call counts.
No. It only estimates bandwidth capacity. Trunk, license, SBC, or platform limits may be lower.
It is the percentage of the stated VoIP bandwidth you are willing to consume in normal planning, leaving the remainder as reserve.
Yes. VoIP is bidirectional. A constrained upstream path can be the limiting direction even when downstream capacity is larger.