Turn call volume into concurrent lines.
Average traffic hides the burst. Model monthly calls, handle time, business hours, and your peak-to-average ratio to size a safer concurrency limit.
formula
Concurrency is occupied minutes divided by available minutes
Monthly call minutes are spread over your operating window, then multiplied by a peak factor. The result is rounded up because partial lines cannot accept calls.
average concurrency = calls × handle time ÷ (hours × days × 60)
required lines = ceil(average concurrency × peak factor)
This is a planning estimate, not a queueing simulation. For strict answer-time SLAs, add arrival-rate distributions, abandonment, retry behavior, and Erlang-C or a discrete-event traffic model.