Erlang C Calculator for Call Centers
Calculate the optimal number of agents needed to meet your service level targets based on call volume and average handle time.
Erlang C Calculator
Enter your call center metrics to calculate the optimal number of agents needed.
What is the Erlang C Formula?
Erlang C is a mathematical formula used to determine the probability that a call will have to wait in a queue and the number of agents needed to handle a given call volume. Named after Danish mathematician Agner Krarup Erlang, this formula is fundamental in call center workforce planning.
The formula takes into account three key variables: the number of calls per hour, the average handle time per call, and the target service level. It then calculates the minimum number of agents needed to meet that service level target.
Key Inputs
- Calls per Hour: The average number of incoming calls your center receives per hour.
- Average Handle Time (AHT): The average duration of a call in seconds, including talk time, hold time, and after-call work.
- Service Level Target: The percentage of calls you want answered within a target time (e.g., 80% of calls answered within 20 seconds).
- Target Answer Time: The number of seconds within which you want calls to be answered.
Key Outputs
- Agents Needed: The minimum number of agents required to meet your service level target.
- Service Level: The percentage of calls that will be answered within the target time.
- Average Speed of Answer: The average time a caller will wait before being connected to an agent.
- Probability of Waiting: The likelihood that an incoming call will not be answered immediately.
- Traffic Intensity (Erlangs): The total workload in Erlangs, representing the number of hours of call work per hour.
- Agent Occupancy: The percentage of time agents are busy handling calls versus idle.
Why Erlang C Matters for Call Centers
Staffing is one of the biggest cost drivers in any call center. Too many agents means wasted resources. Too few means long wait times, unhappy customers, and missed SLAs. The Erlang C formula helps you find the right balance.
Predict Staffing Needs
Use historical call data to determine exactly how many agents you need for each shift and time slot.
Reduce Wait Times
Ensure enough agents are available to handle peak call volumes without excessive customer wait times.
Control Costs
Avoid overstaffing while still meeting your service level targets. Staff efficiently, not excessively.
Meet SLA Targets
Calculate the exact staffing needed to consistently hit your service level agreements.
Tips for Using the Erlang C Calculator
Use real call data
The more accurate your input data, the more reliable the results. Use actual call logs rather than estimates whenever possible.
Account for shrinkage
Agents are not available 100% of the time due to breaks, training, and meetings. Add a shrinkage buffer (typically 10-30%) on top of the calculated agent count.
Run multiple scenarios
Calculate staffing for different times of day and days of the week. Peak hours will require more agents than quiet periods.
Update regularly
Call patterns change over time. Re-run calculations weekly or monthly to keep staffing aligned with actual demand.
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