Erlang C Calculator for Call Center Staffing
Calculate exactly how many agents your call center needs to hit your service level targets. Powered by the Erlang C formula — the industry standard for workforce planning.
Start CalculatingCall Center Parameters
Total incoming calls per hour across all lines
Includes talk time + after-call work
% of calls answered within target time. Industry standard: 80%
Maximum wait time in seconds. Standard: 20s
Typical range: 25-35%
Fully loaded cost for monthly cost estimate
Agents Needed
12
8 raw + 4 for shrinkage
88.01%
10s
62.5%
16.73%
83.27%
5 Erlangs
Calculate for Your Industry
Get pre-loaded benchmarks and industry-specific defaults for more accurate staffing calculations.
What is the Erlang C Formula?
The Erlang C formula is a mathematical model used in telecommunications and call center workforce planning to determine the number of agents needed to handle a given call volume at a desired service level. Developed by Danish mathematician A.K. Erlang in the early 20th century, it remains the industry standard for contact center staffing calculations.
Unlike simpler calculations that just divide call volume by agents, Erlang C accounts for the random nature of call arrivals. Calls don't arrive in a perfectly even pattern — they cluster and spread unpredictably. Erlang C models this randomness using Poisson distribution, giving you a much more accurate staffing recommendation than basic arithmetic.
The formula calculates the probability that a caller will need to wait in a queue, given the number of available agents and the traffic intensity (measured in Erlangs). From this, we can derive key metrics like service level, average speed of answer, and agent occupancy.
How to Use This Calculator
- 1
Enter your call volume
Input the number of calls your center receives per hour. Use your peak-hour volume for conservative staffing, or your average for baseline planning.
- 2
Set your Average Handle Time (AHT)
This is the total time from when an agent picks up a call to when they complete after-call work. It includes talk time, hold time, and wrap-up time.
- 3
Define your service level target
Most call centers target 80/20 — meaning 80% of calls answered within 20 seconds. Adjust based on your business requirements.
- 4
Adjust shrinkage
Shrinkage accounts for time agents aren't available: breaks, training, meetings, sick days, and other off-phone activities. Typical ranges are 25-35%.
- 5
Review your results
The calculator shows the minimum agents needed, plus key metrics like occupancy, ASA, and probability of wait. Add a cost per agent for monthly staffing estimates.
Understanding Your Results
Service Level
The percentage of calls answered within your target time. Higher is better — most centers target 80% or above.
Average Speed of Answer (ASA)
The average time callers wait before being connected to an agent. Lower is better — under 20 seconds is ideal.
Occupancy
How busy your agents are. 80-85% is the sweet spot. Above 90% leads to burnout; below 70% may indicate overstaffing.
Probability of Wait
The chance that any given caller will need to wait in queue before reaching an agent.
Traffic Intensity (Erlangs)
A measure of total call workload. Calculated as calls per hour multiplied by average handle time, divided by 3600.
Immediate Answer %
The percentage of callers who are connected to an agent instantly with zero wait time.