📞 Call Wait Time Calculator
Enter your call volume, average handle time, interval, and agent count to model a call queue with Erlang C — offered load, probability of waiting, average speed of answer, and service level.
📊 Model the Queue with Erlang C
📊 Queue metrics (Erlang C)
What is a Call Wait Time Calculator?
It applies the Erlang C queueing model — the industry standard for contact-centre planning — to your traffic. Give it the calls in an interval, the average handle time, the interval length, and how many agents are on, and it returns the offered load in Erlangs, the chance a caller waits, the average speed of answer, and the service level against your answer-time target.
Workforce planners use it to see how a given roster will perform under a forecast call volume, to test how sensitive wait times are to one more or one fewer agent, and to spot an understaffed interval before it turns into abandoned calls. To work the other way — from a target back to a headcount — use the staffing calculator.
❓ Frequently Asked Questions
What is the Erlang C formula?
Erlang C models a call queue where callers wait rather than being turned away. From the offered load (calls × average handle time ÷ interval, measured in Erlangs) and the number of agents, it gives the probability that an arriving call has to wait, from which the average speed of answer and the service level follow.
What is offered load, in Erlangs?
One Erlang is one hour of call traffic per hour — i.e. one agent kept continuously busy. If you take 100 calls of 180 seconds each in a 30-minute interval, that is 100 × 180 ÷ 1800 = 10 Erlangs of offered load, so you need more than 10 agents just for the queue to be stable.
Why must the number of agents exceed the offered load?
If agents only match the offered load, they are 100% occupied and the queue grows without bound — the wait becomes infinite. Erlang C requires agents strictly greater than the load; the calculator flags an understaffed configuration where that condition fails.
What is service level and ASA?
Service level is the percentage of calls answered within a target time, such as 80% within 20 seconds. Average speed of answer (ASA) is the mean wait across all callers, including those answered immediately. Both drop sharply as occupancy climbs toward 100%, which is why a small change in staffing has a large effect.