Calculator Inputs
Example Data Table
| Scenario | Calls | Interval | AHT | Target | Shrinkage | Use Case |
|---|---|---|---|---|---|---|
| Support Desk | 350 | 30 minutes | 240 seconds | 80% in 20 seconds | 30% | Daily staffing review |
| Sales Queue | 180 | 30 minutes | 300 seconds | 85% in 15 seconds | 25% | Revenue queue planning |
| Technical Help | 120 | 15 minutes | 420 seconds | 75% in 30 seconds | 35% | Complex issue coverage |
Formula Used
Offered Load:
A = Calls × Average Handle Time ÷ Interval Seconds
Erlang C Probability of Waiting:
C(N,A) = [(AN ÷ N!) × N ÷ (N − A)] ÷ [Σ(Ak ÷ k!) + (AN ÷ N!) × N ÷ (N − A)]
Service Level:
SL = 1 − C(N,A) × e−(N − A) × Target Time ÷ AHT
Average Speed of Answer:
ASA = C(N,A) × AHT ÷ (N − A)
Occupancy:
Occupancy = Offered Load ÷ Agents × 100
Scheduled Agents:
Scheduled Agents = Required Productive Agents ÷ (1 − Shrinkage)
How to Use This Calculator
- Enter the forecasted call count for the selected interval.
- Enter the interval length in minutes.
- Add average handle time in seconds.
- Set the target answer time and service level.
- Add shrinkage for breaks, meetings, coaching, and absence.
- Enter maximum occupancy to protect agent workload.
- Add current agents when you want a staffing gap.
- Press the calculate button and review the result above the form.
- Use CSV or PDF export for reporting.
Call Center Erlang Planning Guide
Why Erlang Planning Matters
Call centers need careful staffing decisions. A small mistake can change customer wait time. Too few agents create queues. Too many agents increase labor cost. An Erlang calculator helps balance both sides with a structured model.
How Traffic Is Measured
This calculator uses call volume, average handle time, and interval length. It converts those inputs into offered load. Offered load is measured in Erlangs. One Erlang means one agent is busy for a full interval. Ten Erlangs means ten agents are continuously busy during that period.
What Erlang C Shows
The main result is based on Erlang C. This model estimates the chance that a caller must wait. It also estimates service level, average speed of answer, and occupancy. These values help managers compare staffing choices before publishing a schedule.
Why Shrinkage Is Included
A useful plan should not stop at raw agent demand. Real teams have breaks, meetings, coaching, and absence. Shrinkage adjusts the staffed number for those losses. The calculator divides required productive agents by the available percentage. This gives a practical scheduled agent count.
Why Occupancy Needs Control
Occupancy is also important. High occupancy may look efficient. Yet very high occupancy can create stress. It can reduce recovery time between calls. The calculator checks the maximum occupancy target. This prevents a plan from looking good only by overloading staff.
Understanding Service Level
Service level measures the percent of answered calls within a target time. A common target is eighty percent within twenty seconds. Different centers may choose different targets. Sales, support, medical, and emergency desks often need different goals.
Reading Queue Results
Average speed of answer gives another view of queue behavior. It shows the expected waiting time across calls. Probability of delay shows how often callers may enter a queue. These measures help explain why service level changes when staffing changes.
Using Patience Risk
The optional patience field gives a simple risk view. It estimates the share of callers still waiting beyond a patience limit. This is not a full abandonment model. It is a planning indicator based on the Erlang C waiting curve.
Final Review
Use the result as a planning guide. Review historical arrival patterns first. Check seasonality and marketing activity. Validate handle time from recent reports. Then compare current agents with required agents. Export the result when you need a record. Share the CSV or PDF during workforce review sessions.
FAQs
What is an Erlang in call center planning?
An Erlang is one full unit of workload. It means one agent is busy for the full interval. The calculator finds Erlangs by multiplying call volume by average handle time, then dividing by interval seconds.
What does Erlang C calculate?
Erlang C estimates queue delay when calls arrive randomly and agents handle one call at a time. It predicts delay probability, service level, occupancy, and average speed of answer.
Why is shrinkage important?
Shrinkage covers time agents are paid but not available for calls. Breaks, training, coaching, meetings, and absence reduce coverage. Adding shrinkage gives a realistic scheduled staff number.
What is service level?
Service level is the percentage of calls answered within a chosen time. For example, 80% in 20 seconds means eight out of ten calls should be answered within twenty seconds.
What is average handle time?
Average handle time is the average call duration plus related after-call work. It is entered in seconds. Higher handle time increases offered load and usually requires more agents.
What is occupancy?
Occupancy shows how much productive agent time is used by call workload. Very high occupancy may reduce idle time, but it can also increase stress and service instability.
Can this calculator predict abandonment?
It gives a simple patience risk estimate. It is not a full abandonment model. Use it as a planning signal, not as a final abandonment forecast.
Why does one extra agent change the result?
Queues are sensitive near capacity. When traffic is close to available agents, one extra agent can reduce delay sharply. This is a normal Erlang C behavior.