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Call Center Staffing Calculator (Erlang C)

How many people do you need answering phones to keep callers from waiting? This calculator uses the Erlang C formula, the standard model used by call centers, to estimate staffing from your busiest hour's call volume and average call length.

min

Talk time plus any after-call work.

sec
%

Example values

People needed on the phones

4

Average wait to answer
20.9 sec
Callers who wait at all
17.4%
Calls answered in target
85.3%
How each person's hour is spent (4 on the phones)
  • On calls30 min50%
  • Waiting for the next call30 min50%

These are example values, not industry figures. Adjust the controls to match your business.

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How it works

Workload in Erlangs = calls per hour × average call length in hours. The calculator then finds the smallest number of people for which the Erlang C probability of waiting, combined with your target answer time, meets your service-level target. Average wait = probability of waiting × call length ÷ (people − workload).

Erlang C assumes callers wait rather than hang up, so plan for your busiest hour and treat the result as an estimate. When peaks are short and sharp, like a storm day, see the storm call surge playbook.

Frequently asked questions

What is Erlang C?

A queueing formula that estimates the probability a caller has to wait, given the number of calls, how long they last and how many agents are available. It's widely used to plan call center staffing.

What are Erlang C's limitations?

It assumes callers wait in a queue rather than hanging up, and that calls arrive randomly. Real callers do hang up, so treat the result as a planning estimate, and plan for your busiest hour, not your average one.