Call Center Staffing (Erlang C)
Calculate call center agent requirements using Erlang C formula. Enter values for instant results with step-by-step formulas.
Worked Examples
Example 1: Standard Inbound Center
Problem: 120 calls/hour, 5-minute (300s) average handle time. Target: 80% in 20 seconds. 30% shrinkage.
Solution: Traffic: 10 Erlangs. Required: 14 agents for 80% SL. With shrinkage: 20 FTE scheduled. Occupancy: 71%. Healthy operation.
Result: 14 agents | 20 FTE | 80% SL | 71% occupancy | Optimal
Example 2: High-Volume Sales Center
Problem: 300 calls/hour, 4-minute (240s) handle time. Target: 90% in 15 seconds. 25% shrinkage.
Solution: Traffic: 20 Erlangs. Required: 27 agents for 90% SL. With shrinkage: 36 FTE. Occupancy: 74%. Healthy but expensive.
Result: 27 agents | 36 FTE | 90% SL | High staffing cost
Example 3: Understaffed Support Desk
Problem: 80 calls/hour, 8-minute (480s) handle time. Only 12 agents. 35% shrinkage.
Solution: Traffic: 10.7 Erlangs. 12 agents achieves only 45% SL. Need 15 agents for 80%. Severely understaffed.
Result: 45% SL actual | Need 15 | Critical understaffing | Customer impact
Frequently Asked Questions
What is Erlang C?
Erlang C is a mathematical formula used in call center workforce management to calculate the number of agents needed to achieve target service levels. It accounts for queuing theory—callers waiting in line when all agents are busy. Named after Danish mathematician A.K. Erlang.
What's the difference between Erlang B and Erlang C?
Erlang B assumes no waiting—callers get busy signal if all agents occupied (used in telephony circuits). Erlang C assumes callers queue and wait for available agents (used in call centers). Erlang C is appropriate for staffing where customers wait on hold.
What is shrinkage in call centers?
Shrinkage is the percentage of scheduled time agents aren't handling calls: breaks, training, meetings, absenteeism, after-call work. Typical shrinkage is 25-35%. If shrinkage is 30%, you need to schedule ~143 agents to have 100 available.
What is occupancy in call centers?
Occupancy = time agents spend handling calls / total available time. 85% means agents are on calls 85% of time. Too high (>90%) causes burnout. Too low (<70%) is inefficient. Target 80-85% for balance.
How does handle time affect staffing?
Handle time (talk time + after-call work) directly impacts staffing. Reducing handle time by 10% can reduce staff needs by ~10%. Focus on training, knowledge bases, and process improvement to reduce handle time without sacrificing quality.
What are the limitations of Erlang C?
Erlang C assumes: Poisson call arrivals, consistent handle times, infinite patience (no abandonment), single queue. Real call centers have peaks, variable handle times, and callers who hang up. Use as starting point, then adjust based on real data.