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Erlang Calculator

Calculate call center staffing requirements using Erlang C formula

Call Center
Staffing
Erlang C
Workforce Planning

Call Center Parameters

Expected number of inbound calls per hour

Average duration of call including wrap-up time

Percentage of calls to be answered within target time

Maximum acceptable wait time (e.g., 20 for 80/20 SLA)

Time agents are unavailable (breaks, training, meetings)

About Erlang Calculator

The Erlang Calculator uses the Erlang C formula to determine optimal call center staffing levels. This mathematical model, developed by Danish mathematician A.K. Erlang, is the industry standard for workforce planning in contact centers worldwide.

How it works: The calculator takes your expected call volume, average handle time (AHT), and service level targets to compute the minimum number of agents needed. It also factors in shrinkage (breaks, meetings, training) to give you realistic scheduling requirements.

Key Metrics Explained:

  • Service Level: Percentage of calls answered within your target time (e.g., 80/20 means 80% answered in 20 seconds)
  • Occupancy: How busy your agents are. Ideal range is 80-85% to prevent burnout
  • Traffic Intensity: Call volume expressed in Erlangs (hours of call traffic per hour)
  • Shrinkage: Time agents are paid but unavailable (typically 25-35%)

Use Cases: Perfect for inbound call centers, customer service teams, technical support, sales hotlines, emergency services, and any operation where customers call and wait for available agents. Also useful for queue management and capacity planning.

Privacy: All calculations are performed locally in your browser. No call center data or staffing information is transmitted to any server.

Frequently Asked Questions (FAQ)

What is the Erlang C formula?
The Erlang C formula is a mathematical model used in call centers to calculate the probability that a caller will have to wait for an agent. It helps determine the optimal number of agents needed to meet service level targets based on call volume and average handle time.
What is Average Handle Time (AHT)?
Average Handle Time (AHT) is the average duration of one transaction, measured from when the call is answered until the agent completes all related work. It includes talk time and after-call work. AHT is typically measured in seconds.
What is a good service level target?
A common service level target is 80/20 (80% of calls answered within 20 seconds). However, this varies by industry. Premium services might target 90/15, while cost-conscious operations might use 70/30. Try our Queue Waiting Time Calculator to analyze different scenarios.
What is shrinkage in call centers?
Shrinkage refers to the time agents are paid but not available to handle calls. This includes breaks, meetings, training, and other non-call activities. Typical shrinkage ranges from 25-35%. You need to account for this when scheduling agents.
What is occupancy and what is a healthy rate?
Occupancy is the percentage of time agents spend handling calls versus waiting for calls. While 100% might seem ideal, 80-85% occupancy is healthier as it allows agents breathing room between calls and prevents burnout. Higher occupancy can lead to stress and quality issues.
How accurate is the Erlang C calculator?
Erlang C is very accurate for inbound call centers with random call arrivals and assumes infinite queue capacity. It works best with steady call patterns. For more complex scenarios with abandonment rates or scheduled callbacks, consider more advanced workforce management software.
Can I use this for chat or email support?
While Erlang C was designed for phone calls, it can be adapted for chat support where agents handle one conversation at a time. For email or multi-chat scenarios where agents handle multiple interactions simultaneously, different models like Erlang A might be more appropriate.

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