Email and ticket staffing calculator
Email is a workload problem, not a queueing one: nobody is holding, so you staff to throughput and let a backlog form, as long as no email waits longer than the turnaround target. Enter the daily volume, handle time, turnaround and how peaky the day is, and the calculator finds the capacity you need, the agents to schedule, and the longest wait that staffing produces.
Each staffed day, after shrinkage.
- Agents on task
- 13.9
- Capacity needed
- 62.5/h
- Agents if arrivals were flat
- 13.9
- Longest wait
- 1.0 h
- Backlog at the end of the peak
- 63
- Handling work per day
- 100.0 h
- Agent-hours per day
- 111.1 h
Concurrent agents actually working email.
Set by daily throughput.
For the email at the back of the peak backlog.
Workload ÷ occupancy.
Show the working
- Workload = 500 × 12 min ÷ 60 = 100.0 hours of handling a day.
- Throughput: 500 emails over 8 staffed hours is 62.5 an hour on average; the peak is 1.5 × that, 93.8 an hour, for 2 h.
- Turnaround: with capacity c, the backlog after the peak is (93.8 − c) × 2 h and takes that ÷ c to clear, so c ≥ 93.8 × 2 ÷ (2 + 4) = 31.3 an hour keeps every wait under 4 h.
- Capacity needed = the larger of throughput and turnaround = 62.5 an hour (throughput binds).
- An agent clears 60 ÷ 12 × 0.90 = 4.50 emails an hour, so 62.5 ÷ 4.50 = 13.89 agents on task.
- Shrinkage: 13.89 ÷ (1 − 0.10) rounds up to 16 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 email staffing with a turnaround time is calculated
Nobody waits on hold for an email, so the Erlang queue is the wrong model. What matters is throughput: can the team clear the day's work, and can it do so without any email waiting longer than the turnaround target? The first is daily volume divided by staffed hours. The second depends on how bunched the arrivals are.
The calculator describes the day with a peak factor (busiest hour divided by the average hour) and a peak length. If capacity is set at the average, a backlog builds during the peak and drains afterwards, and the email at the back of it waits the longest. The turnaround target caps that wait, which sets a minimum capacity: peak rate × peak length ÷ (peak length + turnaround). A long turnaround lets you staff close to the average; a short one pushes you towards the peak.
Capacity is converted to agents through handle time and a target occupancy, which for email can be higher than for voice because there is always work waiting. Shrinkage then turns agents on task into agents to schedule. The result is a daily figure; to get FTE, multiply by staffed days and divide by contracted hours, the same way the week planner does for voice.
Read the full guide: How to staff an email queue with a turnaround time
Frequently asked questions
- Can I use Erlang C for email by setting a long target answer time?
- You can, and with a target of hours against a handle time of minutes Erlang C collapses to the throughput answer, so it is not wrong. But it cannot tell you anything about the turnaround, because it assumes arrivals are steady inside the interval and nothing carries over. This model does the same throughput sum and then adds the backlog behaviour the turnaround actually depends on.
- How do I find my peak factor?
- From an hourly volume report: divide the busiest hour's volume by the average hourly volume across staffed hours. 1.3 to 1.8 is typical for inbound email; the peak length is how many hours sit near that level. If arrivals are spread across 24 hours but staffing is not, the overnight accumulation behaves like an extra peak at opening time.
- What occupancy should I use for email?
- Higher than voice, because there is no idle waiting for the next contact: 85 to 90 per cent is common. Going to 100 per cent assumes no wrap, no system delay and no switching cost, and in practice produces the same fatigue voice occupancy does.
- What about emails that need more than one touch?
- Count each touch as an email with its own handle time, or fold the expected number of touches into the handle time. A reply that generates a follow-up is new work arriving later, and it belongs in the volume, not the turnaround.
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