Erlang C staffing calculator
How many agents does this interval need?
The Erlang C model is how contact centres have sized intervals for a century. Enter the demand and the target, and it finds the smallest headcount that meets both your service level and your occupancy cap.
All free toolsYour numbers
Talk plus after-call work.
The % of contacts answered inside the target time.
Paid time not available for contacts.
The busiest you are willing to run agents.
The formula
How this is calculated.
- 1Workload in erlangs = contacts × AHT ÷ interval length
- 2Find the smallest headcount whose Erlang C service level meets the target
- 3Add agents until occupancy sits under the cap
- 4Rostered agents = agents on contacts ÷ (1 − shrinkage)
Before you trust it
What this model assumes.
- Erlang C assumes nobody abandons the queue and everyone waits as long as it takes. Real queues abandon, so for long waits Erlang C overstates the staff you need.
- It assumes arrivals are random and steady across the interval. A scripted campaign or an outage spike breaks that.
- It sizes one interval in isolation. A roster still has to join those intervals into shifts people can actually work.
This runs entirely in your browser — nothing you type is sent to us. It is arithmetic on your own figures, not a benchmark or a recommendation.
In the platform
Where WFMPro does this for you.
These tools answer one question at a time, from numbers you type in. WFMPro runs the same maths continuously against your live data.
Run this on your own data with us.
A working session on your forecasts, schedules and shrinkage — and where WFMPro would take it from there.