Free Erlang C Calculator for Call Center Staffing

Call center shrinkage is the percentage of scheduled time when agents are unavailable to handle calls – covering breaks, training, meetings, and absences. The industry average sits at 25–35%. A call center shrinkage calculator or a tool like this one accounts for it automatically. Without it, your staffing numbers will always fall short in practice.

Average handle time (AHT) combines talk time, hold time, and after-call work. Higher AHT increases the agent headcount needed to hit your service level, making it the most impactful variable in any call center staffing calculation.

All three are staffing models from queuing theory. Erlang B calculates trunk lines needed. If all lines are busy, the call is dropped. Erlang C calculates agents needed. If all agents are busy, the caller waits. Erlang A adds one layer of realism to Erlang C by accounting for callers who hang up while waiting.

Multiply call volume by AHT to get total workload hours, then divide by the productive hours one agent works. Finally divide by (1 – shrinkage rate) to get your real-world headcount. Example: 10 base agents at 30% shrinkage = 10 / 0.70 = 14.3 FTE required.

The 80/20 rule means 80% of inbound calls should be answered within 20 seconds. It is the industry standard service level benchmark used to balance customer wait times against staffing costs. Some industries apply stricter or more relaxed targets based on call complexity.

This staffing calculator is built for inbound queuing environments where callers wait for an available agent. For outbound call center staffing, the Erlang C model does not apply. Outbound teams use a simpler occupancy-based formula instead. If you run both inbound and outbound, calculate each separately.

calculator to get your base agent count for your service level target. Then divide by (1 minus your shrinkage rate) to get your real-world headcount.

Multiply call volume by average handle time to get traffic intensity in Erlangs. Feed that into the Erlang C formula to get the probability of waiting. In practice the math is too complex to do manually. That is exactly what this calculator is for.

Enter your call volume, AHT, service level target, and shrinkage rate. The calculator converts those inputs into traffic intensity in Erlangs, applies the Erlang C formula, and returns the minimum agent count needed to meet your target.

Four inputs: call volume per interval, average handle time (AHT), target service level, and your shrinkage rate. That is everything the calculator needs to return your required headcount.

Yes. Erlang C is the industry standard for inbound call center staffing. It works best when callers queue and wait for an agent. If your call center has a high abandonment rate, Erlang A gives more accurate results as it accounts for callers who hang up.

The formula itself is mathematically exact. In practice it tends to overestimate staffing slightly because it assumes callers wait indefinitely and never hang up. For classic inbound call centers with low abandonment it is highly reliable. For high abandonment environments, Erlang A gives more accurate results

The main limitation is that it assumes callers wait indefinitely and never hang up. This means it often overestimates the headcount you need. It also assumes a constant call arrival rate, so sudden volume spikes within an interval will not be reflected in the results. For most inbound call centers it remains a reliable baseline. For environments with high abandonment, Erlang A gives a more realistic output.