Call Center Staffing Calculator (Erlang C)
Work out how many agents a phone queue needs with the Erlang C formula. Enter call volume, handle time, target service level and shrinkage to get a schedule.
Call center staffing usually comes from last quarter's budget, not this week's call volume. Too few agents and hold times climb, calls abandon, and the same callers ring back within the hour. Too many and the extra seats sit idle between peaks, a cost nobody can point to a benefit for. The honest number sits between the two, and it depends on how bursty your call arrivals are, not just how many you get on average.
This calculator runs the Erlang C formula, the queueing model call centers have used for staffing since before software did the arithmetic. Enter calls per hour, average handle time, the service level and answer time you're targeting, and your shrinkage rate. It returns agents needed on the phones, agents to schedule once shrinkage is added back, occupancy, and the service level and average speed of answer that staffing level actually produces. It runs in your browser; nothing you type is sent anywhere.
Erlang C: traffic = calls per hour × handle time; agents are added until the target service level holds. Scheduled = floor ÷ (1 − shrinkage). Nothing you enter leaves your browser.
This ran in your browser on what you typed. The product runs on your actual calls, chats and emails.
Take the peak off this number — start freeWhat each input means
- 01
Calls per hour
The arrival rate for the hour you're staffing, not a daily average — usually your busiest hour. Pull it from your ACD or telephony report; if volume swings a lot across the day, run this once per hour block rather than once for the whole day.
- 02
Average handle time (seconds)
Talk time, hold time and after-call work added together, in seconds. Your telephony report or the average handle time calculator gives you this number; use the true average, not a target you're hoping to hit.
- 03
Target service level (% of calls answered within the target time)
The share of calls you want answered inside the answer-time target below — 80% is the common default, but your contact center's existing target is the right number to use if you have one.
- 04
Target answer time (seconds)
The wait time paired with the service level above, commonly 20 or 30 seconds. Together they read as 80% of calls answered in 20 seconds — use your own target if support already has one.
- 05
Shrinkage (% of paid time agents are unavailable: breaks, training, meetings)
Everything that takes an agent off the phones while they're still being paid: breaks, training, coaching, meetings, sick time you couldn't plan around. 30% is a common starting estimate; your workforce management tool has the real figure if you track it.
Questions about this tool
It's a formula for how many agents a queue needs when calls arrive randomly rather than evenly spaced. Feed it call volume and handle time and it tells you the odds a caller waits at all, and how long the wait gets, for any given number of agents. Staffing is then the smallest number of agents that keeps that wait inside your target.