Erlang C Staffing Calculator
How Many Agents Does Your Call Center Need?
Use the Erlang C calculator to size your contact center team. Enter your call volume, average handle time, and service level target to find the number of agents required - then make every one of those calls count with AI QA.
Erlang C Staffing Calculator
Agents Required
to hit your service level
Occupancy
agent utilization
Avg. Speed of Answer
average wait time
Staff the calls - then make every one count.
Once you've staffed 17 agents, Voxjar evaluates 100% of their calls automatically for QA, compliance, and coaching.
How It Works
What Is an Erlang C Calculator?
An Erlang C calculator tells you how many agents your contact center needs to answer its calls within a target service level.
It's based on the Erlang C queuing formula, developed from the work of Danish mathematician A. K. Erlang. The model accounts for two realities of inbound calling: calls arrive randomly, not evenly, and when every agent is busy, callers wait in a queue. That makes it far more accurate than simply dividing total call minutes by agent hours.
How to Use This Calculator
Enter five inputs:
- Calls in period and period length - your call volume over a window (often your busiest 30 or 60 minutes).
- Average handle time - talk time plus after-call work, in seconds.
- Service level target - the share of calls you want answered in time (e.g. 80%).
- Target answer time - the deadline for that target (e.g. 20 seconds).
The calculator returns the agents required, your projected occupancy (how utilized those agents are), and your average speed of answer.
Staffing Is Only Half the Equation
Erlang C answers "how many agents do I need to pick up the calls?" It says nothing about what happens once those calls connect - whether agents follow compliance scripts, resolve the issue, or represent your brand well.
Most teams measure that with manual QA on a 1–2% sample, leaving the other 98% unseen. Voxjar's AI closes that gap by evaluating 100% of your calls automatically against your own criteria - so once you've staffed correctly, you can be confident about quality and compliance on every interaction, not just the ones a supervisor happened to hear.
Frequently Asked Questions
What is the Erlang C formula?
Erlang C is a queuing formula used to calculate how many contact center agents you need to answer a given volume of calls within a target service level. It accounts for randomness in call arrivals and the fact that callers wait in a queue, making it the standard model for inbound call center staffing.
What inputs does an Erlang calculator need?
You need the number of calls in a period, the length of that period, your average handle time (talk time plus after-call work), your target service level (e.g. 80%), and the target answer time (e.g. 20 seconds). From those, Erlang C calculates the agents required.
What is a good service level for a call center?
The most common service level target is 80/20 - answering 80% of calls within 20 seconds. The right target depends on your business; sales and emergency lines often aim higher, while some support queues accept a lower service level to control staffing costs.
Why is agent occupancy important?
Occupancy is the percentage of time agents spend handling calls versus waiting. Very high occupancy (above ~85-90%) leads to burnout and attrition, while very low occupancy wastes payroll. Erlang C lets you see the trade-off between service level, staffing, and occupancy.
How does staffing relate to call quality?
Staffing determines whether calls get answered; quality determines what happens on them. Once Erlang C tells you how many agents to schedule, Voxjar evaluates 100% of those agents' calls automatically - so you protect both service level and quality without adding QA headcount.
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Staff smart. Then evaluate every call automatically.
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