Free Tool · Erlang C Model
Contact Center Staffing Calculator
Enter your call volume, handle time, and service level target to calculate how many agents you need — using the same Erlang C model built into every enterprise workforce management system.
Industry standard: 80% of calls answered within 20 seconds
How this calculator works
The Erlang C formula
This tool uses Erlang C — the same formula used in Genesys, NICE, Verint, and every major WFM platform. It calculates the probability that an arriving caller will have to wait, then derives what service level you'll achieve at each agent count.
The iterative Erlang B → C calculation avoids floating-point overflow at high agent counts, so results are accurate for small teams and large call centers alike.
What this calculator doesn't include
Shrinkage: agents needed on phones ≠ agents to schedule. Add 25–35% for breaks, lunch, training, and absence. Divide "agents on phones" by your productive percentage (e.g., 70% = ÷0.70).
Interval analysis: staffing needs change by 30-minute interval. For production planning, run this calculation for each half-hour interval across your operating hours.
Frequently asked questions
What is Erlang C and why does it matter?
Erlang C is a formula developed by A.K. Erlang in 1917 to model telephone traffic. It calculates call wait probability given agent count and call volume. Contact centers use it because simply dividing calls by handle time ignores the randomness of arrivals — Erlang C accounts for that variability, which is why it's the industry standard for staffing.
What is a good utilization rate?
Target 80–85% for inbound queues. Above 85%, small volume spikes cause disproportionate queue buildups — a 10% volume increase at 85% utilization can triple wait times. Below 75%, you're paying for significant idle capacity. Outbound-only teams can run 90%+ since they control dial pace.
What is the industry standard service level?
The "80/20" benchmark — 80% of calls answered within 20 seconds — is the most common target. It originated from 1980s AT&T research and became the default in most contact center SLAs. Healthcare and high-value customer segments often use 90/20. Lower-priority queues sometimes use 80/30.
What are Erlangs (traffic load)?
Traffic load in Erlangs = (calls per hour × AHT in minutes) / 60. It represents the minimum agents if calls arrived perfectly evenly. Since real calls are random, you always need more agents than the Erlang figure. A load above 40 Erlangs typically warrants dedicated WFM software for interval-level forecasting.
How do I convert "agents on phones" to scheduled headcount?
Divide by productive time percentage. Most contact centers see 25–35% shrinkage (breaks, lunch, coaching, training, absence). At 30% shrinkage: productive time = 70%, so scheduled headcount = agents needed ÷ 0.70, or multiply by 1.43. A team needing 20 agents on phones needs roughly 29 scheduled agents.