Guides

How many agents do you actually need?

Free contact centre staffing calculator. Powered by the Erlang C formula, the same maths behind every enterprise WFM system. No login. No spreadsheet. Just answers.

Staffing Calculator

How many agents do you need to hit your service level? Adjust inputs and results update instantly.

seconds (e.g. 3 min = 180)
30%
30% = 7 out of 10 rostered agents available. What is shrinkage?
85%
85% = ~9 min breathing room per hour
You Need
—
agents (after shrinkage)
Erlang C (raw)
—
before shrinkage
Service Level
—
of calls in target
Occupancy
—
agent utilisation
Avg Wait
—
seconds in queue
(optional) Enter your current headcount to see if you're covered.
Enter your call volume and handle time above to get a staffing recommendation.

Day Planner

See how many agents you need across the day. Settings are pulled from the Calculator tab.

First time? Get set up in 2 minutes.
We'll walk you through entering your call volume, handle time and service level target. No jargon, no guesswork.
Shape:
Total Calls: 0
Peak Agents: 0
Avg Agents: 0
Agent-Hours: 0
Enter your headcount to see where you're exposed.
Set your operating hours and daily call volume above. Pick a distribution shape or edit intervals manually.
TimeCallsAgentsOcc %

What formula does this use?

This tool uses the Erlang C formula, the global standard for contact centre staffing. It was created in 1917 by Danish mathematician A.K. Erlang and is built into every major workforce management system in the world, including NICE, Verint, Genesys and Calabrio.

When you use this tool, you're using the same maths that powers enterprise WFM software costing tens of thousands of dollars. The formula itself is open, proven and has been validated for over 100 years.

Why does this matter? The staffing numbers this tool gives you aren't guesses. They're mathematically derived from your actual call volume and handle time.

How does it work?

Calls arrive randomly. Even if you average 100 calls per hour, you might get 12 in one five-minute window and 3 in the next. This randomness means you need more agents than a simple "calls divided by capacity" calculation suggests.

The Erlang C formula models this randomness. Given your call volume, handle time and service level target, it calculates the probability that a call will wait in queue, then finds the minimum agents needed to keep that probability below your target.

On top of the raw calculation, this tool factors in shrinkage (agents unavailable due to breaks, meetings and leave) and maximum occupancy (how busy agents should be before burnout becomes a risk).

Traffic Intensity (Erlangs):
  A = (Calls x AHT) / Interval Length
  Example: (100 calls x 180s) / 1800s = 10 Erlangs

Erlang C - Probability of Waiting:
  P(wait) = [A^N/N! x N/(N-A)] / [Sum(k=0..N-1) A^k/k! + A^N/N! x N/(N-A)]
  Where: N = agents, A = traffic intensity

Service Level:
  SL = 1 - P(wait) x e^(-(N-A) x TargetTime/AHT)

Average Speed of Answer:
  ASA = P(wait) x AHT / (N - A)

Occupancy:
  Occ = A / N

After shrinkage:
  Adjusted = Raw Agents / (1 - Shrinkage%)

What it doesn't cover

No model is perfect. Being upfront about limitations builds trust in the results:

Assumes random arrival. If your calls are scheduled (callbacks, outbound), the formula overestimates. It works best for inbound, unscheduled contacts.

Single-skill only. Erlang C models one queue. Multi-skill or skill-based routing needs more complex modelling.

Not ideal for chat or email. Agents handle concurrent chats, which breaks the one-at-a-time assumption. Use as a rough guide only for non-voice.

Point-in-time. It tells you how many agents you need for a given call rate. It doesn't tell you how to schedule shifts across a week. That's where the Day Planner and Roster Builder come in.

Go deeper

Practical guides on the concepts behind this calculator, written for team leaders who are figuring this out for the first time.

What is shrinkage in a contact centre?
How to calculate it, what a healthy rate looks like, and the mistake everyone makes.

How many agents do you need in a contact centre?

Staffing a contact centre is a balancing act. Too few agents and callers wait in long queues, abandon calls and leave frustrated. Too many agents and you're paying for people to sit idle. The challenge is finding the number that keeps callers happy without burning through your budget.

Most team leaders start by guessing. They look at yesterday's numbers, add a buffer and hope for the best. That works until it doesn't. A spike in volume, a few people calling in sick, or a team meeting scheduled at the wrong time can blow the whole day open.

The better approach is to calculate your staffing needs using a proven formula. The Erlang C formula takes your call volume, average handle time and service level target, then works out the minimum number of agents needed to keep wait times below your threshold. It accounts for the randomness of call arrivals, which is why simple "calls divided by capacity" maths consistently underestimates the agents you need.

What inputs do you need?

To calculate staffing, you need four numbers from your phone system or ACD reports:

  1. Calls per interval. How many calls your team receives in a 30-minute window. If you only have daily totals, divide by the number of hours you're open and halve the result.
  2. Average Handle Time (AHT). The total time from when an agent picks up to when they've finished all after-call notes. Measured in seconds. Check your ACD reports for the team average.
  3. Service level target. The percentage of calls you want answered within a target time. The industry standard is 80/20, meaning 80% of calls answered within 20 seconds.
  4. Shrinkage. The percentage of rostered time agents are unavailable (breaks, meetings, training, leave, sick days). At 30% shrinkage, only 7 out of every 10 rostered agents are on the phones at any given time. Learn how to calculate yours.

What is the Erlang C formula?

The Erlang C formula was created in 1917 by Danish mathematician A.K. Erlang while working at the Copenhagen Telephone Company. He needed to calculate how many telephone operators were required to handle a given volume of calls without making callers wait too long.

Over 100 years later, the same formula is built into every major workforce management system in the world, including NICE, Verint, Genesys and Calabrio. When you use this calculator, you're using the same maths that powers enterprise WFM software costing tens of thousands of dollars per year.

The formula works by modelling the random arrival of calls. Even if you average 100 calls per hour, the actual pattern is uneven. You might get 15 calls in one five-minute window and 3 in the next. This randomness means you always need more agents than a simple average would suggest. Erlang C calculates exactly how many more.

The calculator on this page adds two practical adjustments on top of the raw Erlang C result: shrinkage (to account for agents who are rostered but not on the phones) and maximum occupancy (to prevent burnout from back-to-back calls with no breathing room).

How to calculate contact centre staffing (step by step)

  1. Gather your call data. Pull the number of calls received per 30-minute interval from your ACD or phone system. If you're planning for a new centre or don't have interval data, start with a daily total and use the Day Planner's distribution shapes to model a realistic curve.
  2. Find your AHT. Look for "Average Handle Time" in your ACD reports. This should include talk time plus after-call work (wrap-up, notes, follow-ups). If you're not sure, 180 seconds (3 minutes) is a reasonable starting point for many service teams.
  3. Set your service level target. Most contact centres aim for 80% of calls answered within 20 seconds (written as 80/20). Some premium services target 90/10. Use whatever your business has agreed to. If nobody has set one yet, start with 80/20.
  4. Enter your shrinkage. This is the gap between who's rostered and who's actually available. At 30%, for every 10 agents on your roster, 3 are unavailable at any time due to breaks, meetings, training, leave or sick days. 30% is a safe default. If you track it precisely, use your actual number.
  5. Check occupancy. Occupancy measures how much of an agent's available time is spent on calls versus waiting for the next one. At 85%, agents get about 9 minutes of breathing room per hour. Push above that and you risk burnout, higher sick leave and increased attrition.
  6. Review the results. The calculator shows how many agents you need (after shrinkage), your predicted service level, occupancy rate and average wait time. If you enter your actual headcount, it will compare what you need against what you have and show you where the gaps are.

Contact centre glossary

Terms you'll see in this calculator and across workforce management.

AHT (Average Handle Time)
The total time an agent spends on a call, including talk time and any after-call work like notes or follow-ups. Measured in seconds.
Service Level
The percentage of calls answered within a target time. Written as two numbers like 80/20, meaning 80% of calls answered within 20 seconds.
Shrinkage
The percentage of rostered time agents are unavailable. Covers breaks, meetings, training, coaching, leave and sick days. At 30%, only 7 of every 10 rostered agents are on the phones. Read the full guide.
Occupancy
How much of an agent's available time is spent handling calls versus waiting for the next one. At 85%, agents get about 9 minutes of breathing room per hour. Above 90% risks burnout.
Erlang C
A mathematical formula from 1917 that calculates the probability of a call waiting in queue, then determines the minimum agents needed to meet a service level target. The global standard for WFM staffing.
ASA (Average Speed of Answer)
The average time a caller waits in queue before being connected to an agent. Under 20 seconds is generally considered good.
Erlangs (Traffic Intensity)
A measure of call traffic. Calculated as (calls x handle time) / interval length. 10 Erlangs means agents are collectively handling 10 calls' worth of work at any moment.
FTE (Full-Time Equivalent)
A unit representing one full-time employee's working hours. Two part-time agents each working 50% of full hours = 1 FTE.

Let's figure out your staffing

This takes about 2 minutes. By the end you'll know exactly how many agents you need. Backed by the same formula used by every major contact centre in the world.

You'll need your call volume and average handle time. If you don't have them, we'll show you where to find them.

How many calls per half hour?

Enter the number of calls your team receives in a typical 30-minute window during your busiest period.

Where to find this: Check your phone system (ACD) reports. Look for "calls offered" or "calls received" per interval. If you only have daily totals, divide by hours open, then halve for a 30-min estimate.

How long is a typical call?

Average Handle Time (AHT): from pickup to finishing after-call notes. Enter in seconds.

= 3m 00s
Quick conversions: 2 min = 120s · 3 min = 180s · 4 min = 240s · 5 min = 300s · 7 min = 420s
Where to find this: Your ACD dashboard. Look for "AHT" or "Average Handle Time." Includes talk time + wrap-up.

What standard do you want to hit?

Service level is the percentage of calls answered within a target time. Pick your company's target or the industry standard.

80/20
Industry standard
80/30
Relaxed
90/10
Premium
What does 80/20 mean? 80% of calls answered within 20 seconds. The most widely used target globally. Use your company's SLA if they have one.

Real-world adjustments

Two factors that close the gap between theory and your actual floor.

30%
What does 30% mean? For every 10 agents on your roster, only 7 are actually on the phones at any time. The other 3 are on break, in a meeting, at training, in a 1:1, on leave or off sick. It covers everything that takes an agent away from the queue, from a 15-minute morning tea to a full day of annual leave. If you're not sure, 30% is a safe starting point.
85%
What does 85% mean? When an agent is logged in and ready, they're either handling a call or waiting for the next one. At 85%, they get about 9 minutes of breathing room per hour. At 95%, it's barely 3 minutes, which means back-to-back calls with almost no gap. That gap matters. It's when agents reset, take a breath and prepare for the next caller. Squeeze it out and quality drops, sick leave rises and people quit.