IVA Ports Calculator

Estimate IVA concurrency and required ports with Erlang B. Enter peak calls, average IVA time, and target blocking to size self service capacity.

Inputs

i
The total number of call attempts expected during your busiest measurement window. Use raw attempts before containment or transfer.
i
The time span over which you measure peak call attempts. Shorter windows capture sharper spikes; 30 minutes is the most common.
i
The mean time each call occupies an IVA port before transferring or ending. Include greetings, menus, and typical self-service usage.
i
Target Blocking in the IVA Erlang calculator means the maximum percentage of calls you're willing to have fail to get a port during the busy window. It comes directly from Erlang B theory, which assumes that if all ports are busy, the next attempt is blocked (no waiting, just fails). Here's what the options mean: • P.01 (1%): The calculator will size enough IVA ports so that, at peak load, no more than ~1 in 100 attempts are blocked. This is the most common telecom engineering target. • P.005 (0.5%): Stricter. Only about 1 in 200 attempts should be blocked at peak. Requires more ports than P.01. • P.001 (0.1%): Very strict. Only about 1 in 1,000 attempts blocked. This drives port counts higher and is usually chosen if the business cannot tolerate failed connections.

Results

119 ports
Offered load: 101.640 erlangs. Target blocking: 1.00 percent. Achieved: 0.935 percent.
How this is calculated
  • Attempts in window: 1260.00
  • Arrival rate: 0.700 per second
  • Mean IVA time: 132.0 seconds
  • Offered traffic: 101.640 erlangs
  • Ports N selected so B(N, A) ≤ target; achieved blocking 0.935 percent

Tip: try 15, 30, and 60 minute windows to reflect your peak measurement practice.

Disclaimer

This tool is provided for informational and educational purposes only. Calculations are based on standard Erlang formulas and user-supplied inputs. Results are estimates and should not be relied on as the sole basis for capacity planning or financial decisions. ULAP Tools makes no guarantees of accuracy and assumes no liability for decisions made using this calculator. Always validate results against your own traffic studies and vendor guidance.

FAQ

What is Erlang B used for in call centers?

Erlang B is a formula used to calculate the number of concurrent lines or ports needed to handle peak traffic with a specific probability of blocking. It's commonly applied to IVR and IVA platforms where calls are blocked if all ports are busy.

What is an IVA or IVR port?

An IVA or IVR port is a concurrent session slot on your self-service system. Each active caller occupies a port. If all ports are full, new callers may hear busy signals or fail to connect.

What does blocking probability (P.01, P.005, P.001) mean?

Blocking probability is the chance that a new call attempt is blocked because no ports are available. P.01 means 1% blocking (1 in 100 calls at peak may be blocked). Lower probabilities require more ports.

How do I calculate how many IVR/IVA ports I need?

You need to know your peak call attempts in a time window, the average time each call stays in self-service, and the acceptable blocking probability. Multiply the arrival rate by the call duration to find the offered traffic in erlangs, then use Erlang B to find the required ports.

What is the difference between Erlang B and Erlang C?

Erlang B assumes no waiting — blocked calls are lost. This matches most IVR/IVA platforms. Erlang C models queuing, which is more relevant for live agent staffing.

All calculations are performed locally in your browser. No data is sent to our servers.