Staffing requirement calculator
This calculator runs the full staffing chain for an interval: it finds the Erlang C agents for your service level target, raises the number if that would push occupancy over your ceiling, then grosses it up for shrinkage. The last number is the one that belongs on the roster.
Rostered headcount for this interval, after shrinkage.
- Agents on the phones
- 40
- Erlang C minimum
- 39
- Occupancy
- 83.3%
- Service level achieved
- 87.8%
- Average speed of answer
- 8.6 s
- Workload
- 33.3 erlangs
After the occupancy ceiling.
Before the occupancy ceiling.
Show the working
- Workload = 200 contacts ÷ 30 min × 300 s ÷ 60 = 33.3 erlangs.
- Erlang C: the smallest agent count with a service level of at least 80% within 20 s is 39, at 85.5% occupancy.
- That is above the 85% ceiling, so agents are added until occupancy falls to or below it: 40 agents at 83.3%.
- Shrinkage: 40 ÷ (1 − 0.30) = 57.1, rounded up to 58 to schedule.
Doing this for every interval of the week? Pebble WFM computes the requirement from your forecast and builds the roster. Free month, no card needed.
How the staffing requirement is calculated
Step one is Erlang C: the smallest number of agents whose predicted service level meets the target, given the workload in erlangs.
Step two applies the occupancy ceiling. If the Erlang C answer would leave agents busier than the ceiling allows, the count goes up until occupancy falls to or below it. For a large queue the Erlang answer is already efficient and this step often adds nobody; for a small one it is the ceiling that binds.
Step three grosses the answer up for shrinkage: agents divided by (1 minus shrinkage), rounded up. That is the number to schedule so that, after leave, sickness, breaks and training take their share, enough agents are actually on the phones.
Read the full guide: How to calculate a contact centre staffing requirement
Frequently asked questions
- Is the result a headcount or an FTE?
- It is the number of agents that need to be scheduled for this interval. Headcount and FTE come from doing this for every interval of the week and fitting shifts to the curve. The week planner does the first half of that.
- Which shrinkage figure should I use here?
- Whatever share of scheduled time your agents are not available inside the interval. If you are scheduling against contracted hours, use the full number including leave and sickness. If you schedule against attendance, leave out the external components. The shrinkage calculator splits them.
- Why does the occupancy ceiling change the answer for small teams but not large ones?
- Erlang C gets more efficient with scale. Ten erlangs need 14 agents at 71 per cent occupancy to hit 80/20, while 200 erlangs need 210 at 95 per cent. The ceiling protects small teams from an answer that is mathematically valid but not sustainable.
- How do I do this for a whole week?
- Run it per interval on your forecast, then build shifts that cover the resulting curve. The week planner on this site does the per-interval part and gives you agent-hours and FTE; Pebble WFM does the whole thing from your real data, then builds and publishes the roster.
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