Free Erlang C Calculator for Call Center Staffing
Calculate the optimal number of agents your call center needs to meet your service level targets – powered by the Erlang C formula. Get instant results for headcount, shrinkage, and occupancy. Run as many scenarios as you need and start planning immediately!
Call Center Staffing Calculator
Complete each step to calculate exactly how many agents you need — powered by the Erlang C formula.
What is an Erlang C Calculator?
An Erlang C calculator, often just called an erlang calculator, is a workforce management tool used in call centers to determine how many agents are needed to handle incoming calls while meeting a defined service level target. It is based on the Erlang C formula, developed by Danish mathematician A.K. Erlang in 1917, which models inbound queue behavior to predict staffing requirements with precision.
As a specialized Erlang C calculator for workforce planning, it processes call volume, average handle time (AHT), and a target service level (such as answering 80% of calls within 20 seconds) to return the minimum agent headcount required. Unlike basic staffing ratios, the Erlang C model natural variability and fluctuations of call arrivals, making it the industry standard for call center staffing calculations worldwide.
What are the Benefits of Using a Call Center Staffing Calculator?
With our Erlang C call center staffing calculator, you can:
- Eliminate staffing guesswork: Get a precise agent count based on real call data instead of estimates or gut feel.
- Optimize costs instantly: Avoid overstaffing that wastes budget and understaffing that damages customer experience.
- Hit your service level targets: Calculate the exact headcount needed to meet any SLA commitment and see immediately what it costs to raise the bar.
- Run what-if scenario planning: Simulate volume spikes, AHT changes, or higher shrinkage before they impact your operation.
- Keep agents productive without burning them out: Find the staffing level where agents stay busy enough to justify the cost but have enough breathing room to perform.
How Does an Erlang C Calculator Work?
Input Your Call Metrics
Enter your call center data, such as call volume per interval (e.g., calls per hour), average handle time, target service level (for instance, the percentage of contacts handled within a specific timeframe), and your agent shrinkage rate.
Calculate Staffing Needs
The Erlang C formula runs instantly. The calculator converts inputs into traffic intensity in Erlangs, then iterates through agent counts until it finds the minimum number required to meet your service level target.
Build Your Staffing Plan
Get your staffing results – raw agents needed, total headcount after shrinkage, and agent occupancy rate. All figures are ready to use directly in your workforce plan.
Ready to get started?
Join over 5,500+ modern companies that already trust CloudTalk to have MORE and BETTER calls.
Frequently asked questions
Here is a practical, step-by-step worked example showing how call volume, handle time, service level targets, and shrinkage combine to determine required headcount.
1. Input Parameters:
- Call Volume: 100 calls per hour
- Average Handle Time (AHT): 3 minutes (180 seconds)
- Target Service Level: 80% of calls answered in 20 seconds
- Shrinkage Rate: 30%
2. Calculation Steps:
- Step 1 (Calculate Traffic Intensity): Multiply 100 calls by 3 minutes to get 300 call minutes per hour. Divide by 60 minutes in an hour to get 5 Erlangs of total call workload.
- Step 2 (Determine Base Agents): Applying 5 Erlangs to the Erlang C formula for an 80/20 target returns a minimum of 8 base agents active on the phone (yielding an 88% service level).
- Step 3 (Factor in Shrinkage): Divide base agents by (1 - 0.30) to account for breaks, meetings, and PTO: 8 ÷ 0.70 = 11.4 total FTEs.
Summary Result: To handle 100 calls per hour while meeting your 80/20 target service level, you need to schedule 12 total agents.
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.
Don't know your AHT? Total handling minutes ÷ number of calls in the same period = AHT. You can also use our free AHT calculator to easily determine your exact handle time before calculating staffing requirements.
All three are staffing models from queuing theory. Erlang B calculates trunk lines needed. If all lines are busy, the call is dropped (o ensure your internet connection can support your required active lines, test your network capacity using our VoIP bandwidth calculator). 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, factoring in their Average Patience (also called Average Time to Abandon / ATA).
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.
No, this tool does not function as an outbound call center staffing calculator. The Erlang C model is built specifically for inbound queuing environments where incoming calls arrive unpredictably and wait in line for an available agent. For outbound call center staffing, queuing formulas do not apply.
Outbound teams
rely on predictive dialer ratios, agent connect rates, and target agent occupancy rather than Erlang calculations. If you want to equip outbound representatives with optimized outreach material, you can quickly build customized pitch templates using our AI sales script generator. If you run a blended contact center, use this Erlang C calculator for your inbound workload and calculate your outbound staffing 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.
Additionally, Erlang C assumes all incoming traffic must be answered by live representatives. If human staffing costs for your required volume are too high, you can evaluate the cost impact of offloading routine calls using our AI voice agent ROI calculator. For classic inbound call centers, Erlang C remains a reliable operational baseline.
An Erlang model is an umbrella term for queuing formulas, such as Erlang C, Erlang A, and Erlang B, used to analyze and predict call center traffic. In workforce management, an Erlang staffing model applies these formulas to determine the exact agent headcount needed to meet service level targets.