In a small contact-center queue, changing call volume or handle time slightly can change the requirement by a whole agent. This worked example shows why.
Inputs and assumptions
- 20 calls in a 30-minute interval
- 240 seconds average handle time, including talk, hold and wrap
- Target: 80% answered within 20 seconds
- 30% shrinkage applied after estimating on-phone staffing
Offered traffic is 20 × 240 ÷ 1,800 = 2.67 Erlangs. Erlang C assumes a simplified steady-state queue with callers waiting rather than abandoning.
Four agents or five?
| On-phone agents | Answered within 20 seconds | Occupancy |
|---|---|---|
| 4 | 66.1% | 66.7% |
| 5 | 86.7% | 53.3% |
Four agents miss the 80% target; five meet it. Staffing uses whole people, so there is no 4.5-agent result for an individual interval. Low occupancy can be consistent with meeting a fast-answer target in a small team.
Apply shrinkage carefully
Five on-phone agents with 30% shrinkage require 5 ÷ (1 − 0.30) = 7.14, rounded up to 8 scheduled agents. This is a planning estimate. If your roster already subtracts breaks and meetings explicitly, separate those activities from other shrinkage assumptions so you do not count the same unavailable time twice.
Use the estimate in a roster
- Calculate requirements by interval rather than using a daily average.
- Check how requirements change when AHT or volume changes.
- Compare required agents with available agents after breaks, meals and meetings.
- Review any remaining shortage before approving the schedule.
Queue routing, abandonment, changing arrival rates and real operating constraints can differ from this model. Check estimates against your own operation; a calculated requirement is not an SLA guarantee.
Continue with our free 15-minute break and meeting coverage example and KPI formula guide.
All figures here are fictional worked examples, independently recomputed before publication.