How to Calculate the Number of Agents Required

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How to Calculate the Number of Agents Required
What is a good method of calculating the number of agents required to handle calls in a given time period.


Call Centre Helper

New Article on How to Calculate the Number of Agents Required
There are two ways to calculate the number of agents you need.

Online Erlang Calculator

*The Method recommended by Call Centre Helper*
You can use an online calculator, such as our free Erlang Calculator for Contact Centre Staffing:

Without an Erlang Calculator

We have now written a comprehensive guide to calculating Staffing numbers - It covers all aspects of how to work out the number of staff that you need

We do recommend that you use a tool though

Use an Erlang Calculator
Here is a really basic calculation:

(Handle Time * Calls) = Basic Seconds required
Seconds required / shrinkage % = Total Seconds actually required
Total required / Working seconds in day = Base FTE

BUT Remember this takes NO account of queuing or contact arrival distribution.

If you want to calculate the number of staff the best option is to use an Erlang Calculator. This is a tried and tested formula to calculate the number of agents needed.

Here is a link to the Erlang C Calculator
If you need to use a spreadsheet, look at this one:

You can just plug your numbers in there.

Planning & Control

Erlang is the Best Way to Calculate Staffing
The reason Erlang is so commonly used in some form is because it does a good job, and is really needed in order to give you meaningful data.

If you have 20 hours of calls you will probably have to schedule 25 hours of time, but without Erlang (or a similar alternative) you won't really know.
@ Applebyd - Should that be Seconds Required / Shrinkage?

Unless you report shrinkage as a number greater than 100% then the calculation is wrong. Traditionally shrinkage is reported as 100% - Non Productive Time is it not, which should give anything between 60-80%?


Call Centre Helper

Guidance for Using Erlang

There are a couple of free excel based Erlang calculators that could do the job for as mentioned earlier.

If you still want to use Erlang, but not a calculator, we have written some useful guides explaining Erlang.

What is the Erlang C formula

This article walks you through the Erlang C formula:

What is the Erlang C formula

This is a beginners guide to the Erlang A formula



@ Kevin thanks for the response.

@Dave I have posted this due to a requirement of my work place... In my previous work place I always used the Erlang method throughout...But thanks for your comment :)

@Jonty...As always Thank you Sir!!!

Actual FTE from Number of Agents in 30 Mins

I have got the number of agents required in every half hour by using the Erlang calculator.

Now I need to come up with the actual number of FTEs required in our contact centre.

I have done the below, but have a feeling that this is not really correct.
= (sum of number of agents required in every half hour)/ 2 to bring it to 1 hour/8 staff working hours a day 'shrinkage'

For example it looks like: 109/2/8/0.77
Could someone throw some light on this please!

Resource Planner/Infrastructure Analyst

Lloyds Banking Group

Use a Headcount model first and then Erlang
I've always regarded this as two separate calculations.
If Erlang says you need 20 agents in a given half hour, then you put 20 on, obviously a bit of smoothing is required through some intervals as the volumes will vary.

Erlang is really for scheduling. I think what you are describing is a headcount model.

The simple way

One simple way is just to add up the total calls each month, multiply by your AHT which then gives you the actual staff hours required.
Then add in an efficiency figure (basically this would be the inverse of your availability).
To that add on a percentage for sickness (use your own actuals), holidays (depends on entitlement, but you would expect 10-15%, then other shrinkage.
I allow 12% for breaks, etc and then a further 8% for Admin (1-2-1's, meetings, etc) These were all cumulative figures - meaning you add on hols, then add on sickness and so on.

Take that result and divide by 147 (assuming your agents work 7 hours, 21 days a month).
What you will have is your overall headcount requirement (albeit just based on 1 month - but repeat to build up a pattern)

With your overall headcount done, then use Erlang to decide on how best to allocate those staff by way of shift patterns, etc.

Hope that's of some use

How to add SLA to the calculation
Thanks so much Scott for the reply,

Could you mention how should I also add the SLA into the calculation?

Let’s say the target answer time is 90/20.

I am not very clear on the efficiency, could you elaborate?

Last thing, our help desk functions 11.5 hours/ 6 days a week whereas staff working hours/days is 8/5 days a week only!

So should I also incorporate this into the calculation?



Resource Planner/Infrastructure Analyst

Lloyds Banking Group

The SLA is built into your scheduling
The SLA is built into your scheduling. One of the Erlang calculators that Jonty pointed you in the direction of would take care of that.

The efficiency part is based on the fact that agents have available time waiting on calls. So if your available time is 10% then add in a 90% efficiency.

Your actual shift patterns shouldn;t affect your headcount requirement too much. It's the same amount of work, but just spread over a different period (which comes back to your scheduling) The 147 figure is just the number of hours that a full time agent would work in a month. It will vary slightly depending on the actual working days, but given that you would never change your headcount month by month, then the figure is accurate enough.


Planning & Control

Shrinkage is Cumulative
@ Scott
Not sure if it would be seen as needlessly complicating it, but some areas of shrinkage are cumulative whilst others aren't. It also may vary from one company to another.

For example (and I'm going to use 10% just to keep this simpler) if an agent is paid for 260 days a year, you would factor in Holiday, taking them down to 234 working days, and then factor Sickness as 10% meaning 23.4 days, ending with 210.6 days.

This would actually translate as a practice where you are allowing agents to be logged as both sick and on holiday simultaneously, as the sickness calculation is reducing the total amount of resource you are loosing for other areas of shrinkage. This would be correct depending on company practice, but some businesses say that is an agent is sick during scheduled holiday then the holiday would be given back to the agent to take at another point, in which case the sickness shrinkage should not impact on the total resource lost due to holiday.

It really varies from one category to the other. Obviously if an agent is on holiday then you wouldn't count breaks for this time, so it would be cumulative, but a day of sickness or holiday typically wont result in their 1-2-1 being cancelled so this would be a larger % of their remaining working time, or else done non cumulatively.

It can take a lot of thinking as to the order it should all be figured out in, to get the actual end result. It might only be a couple of % different, but for large centres this could be hundreds of pounds difference.

Resource Planner/Infrastructure Analyst

Lloyds Banking Group

Shrinkage after holiday and sick abscences
Hi Kevin,
Your points are valid, but if I've read you right that's not actually what I'm doing.
My calculations are based on assuming that (just using fictional figs) 10% of staff are on holiday and on top of that a further 5% are off sick. Then of those remaining available in the workforce, there is an additional shrinkage to be added.

You raise a fair point in that the actual calculations would differ from centre to centre, but this can at best only be an estimate.

I've never seen any headcount model that is more than that due to the variables involved.

What is Working Shrinkage?

I have come across the Term "Working Shrinkage" in a Call centre environment.
What is the definition for this? And what would be the calculation?

Thanks, Lino

Capacity Planning Specialist

Calculating Shrinkage
What Call Centre Shrinkage is:

According to Call Centre Helper Shrinkage is a measurement of anything that takes an agent away from their ability to take customer contacts. For a more in depth look at the definition, look at the article mentioned below.

How to calculate Call Centre Shrinkage

This article should help you with How to calculate contact centre shrinkage:


can anyone tell me whether the below equation is correct for agent calculation.

Total No.of calls * AHT(in secs)/Service Level

Ex 90 calls * 480 / 85%

I tried with this but i'm not getting the answer properly.

Pls let me know.


COO Customer Care


Agent requirement calculation
Hi Shyam,

For agent requirement calculation, divide your workload (calls*AHT) by the number of seconds for the length of interval you need it for.


30 min interval, 90*480/1800

60 min interval, 90*480/3600</p>
This gives you the workload in hours (Erlangs)
In addition you will need to add extra hours for shrinkage and you might want to look at a occupancy number to cater for the random arrival patterns.

You will need to then plug this into an Erlang calculator.

[Editor's note - Here is a link to an Online Erlang staffing calculator ]

Hope this helps!



Analysis on call centre performance

i am preparing an analysis study on call centre performance.

The obstacle i am facing is calculating the actual number of agents required per hour and per day.

The data i have got is (30) mins interval and i am confused on how to calculate the required number of agents for this (30) mins interval from the
Erlang C Calculator using the formula -->

=Agents FTE(Calls, Reporting_period, Average_Call_duration, Service_level_percent, Service_level_time, Shrinkage)

The Agents formula oblige you to insert calls per hour, so how can i convert the calls from half-hour to one hour? should i add every half hour interval together? or shall i multiply each half-hour calls by 2?

My second Obstacle is calculating the required number of agents per day, is there any scientific proven way of doing it?

highly appreciate your help.

Hi guys. Need help please. I read all your comments and help please to know how many agents i need per hour. The call center is open from 6H00 AM to 5H00 PM and the agent shift is of 8.5 with a 1 hour lunch. So basically they are paid 7.5Hours. So for the month for November i got:

1756 calls offered

AHT is 20 mins so 1200 seconds

So i did 1756*1200/3600 and it gives me 585 Hours.

And if i divide 585/150 (150 is 7.5 Hours*20 days of work) it gives me 3.9 agent per hour.

Is this right?


Call Centre Helper

Erlang Calculator
We also have an online Erlang calculator available on the Call Centre Helper website

Help needed.

I have a servicedesk within the IT are handle clients computer issue both over phone and email, how can I calculate the agent needed with erlang as not all incident is solved directly over the phone so the variable as time on phone is nit sufficient.

Any ideas ?


Call Centre Helper

Calculating the staff needed for more than 1 channel
It can be a bit tricky to calculate staffing for a combination of both Calls and Emails.

We are in the process of developing a multi-channel staffing calculator (using simulation) that will help you to develop staffing levels.

Multi-channel calculator

Here is the link to our multi-channel calculator:

In the meanwhile the best bet is to produce a weighted average handling time for both your call and staffing levels and then plug them into our Online Erlang Calculator or into the Excel Based Erlang Calculator

New Article on How to Calculate the Number of Agents Required

[We have now written a comprehensive guide to calculating Staffing numbers -


Call Centre Helper

It\'s easy to work out staff required with an Erlang Calculator
This is quite easy to calculate the number of staff needed with the Erlang Calculator.
You need to work our how many calls you could expect per hour.
You probably need to put this into a spreadsheet as it tends to peak towards 11.00 - 15.00 and is lower at other times.

Once you have the calls per hour you can work out the staff using an Erlang calculator.

I've done this
I've taken this article: and converted it to vbs. Now, I simple run the script and it tells me how many FTEs and even forecasts.


Call Centre Helper

Just pop the figures into an Erlang Calculator

Work days
So what is the actual head do I need to hire if let's say I need 50 agents per day and each of one of them has a 2 day off work.

I've seen a lot about computations regarding shrinkage but it doesn't mention anything about workdays off?

Work days reply
Hi Ruby,
Shrinkage is any time away from doing the day job, so having days off work is included in this.

Say for example you have an allowance of 13.334% for annual leave and an expectation of 3.333% sickness.
This gives you 16.667% (0.16667) shrinkage, or 83.333% (0.83333) useful time.

To calculate staffing you divide your required headcount by useful time:

50 / (1-0.16667) = 50 / (0.8333) = 60 agents required.

Other types of shrinkage call centres usually take into account will include screen breaks, training, coaching, 1-2-1's and team meetings - This is called schedule by exception.
A shrinkage of 30-40% (71-83 agents required) is common in my experience but depends what type of call centre it is.

Actual HC calulation to include Service Level
I currently have a formula, shown below, that calculates HC based on call volume, aht, for 1 hour/ftehrsinamonth and shrinkage:


I'm trying to figure out how to add a target SL of 85%/15seconds to the above to figure optimal headcount without the use of a calculator, need the actual formula.

Thanks for any help!


Call Centre Helper

You have to use an Erlang Calculator
Gary S

Your formula is flawed and will dramatically underestimate the number of people needed as it ignores the random arrival of work.

The only way to get an accurate figure is to use an Erlang Calculator.

Customer service program X is open 24 hours a day and has a backlog of 2,400 e-mails. On average it takes 480 seconds to process an e-mail. They get an average of 90 new e-mails an hour. Assume there are 18 employees each hour assigned to process e-mails who are actually productive (able to do work) 90% of the time. How many hours does it take to get the backlog of e-mails to the level of 1000 e-mails? Show your calculation steps and round the final answer off to a whole number.


Call Centre Helper

Work out the number of emails per employee per day
This is fairly simple.

You just work out the number of emails that one member of staff can handle per hour.

So if there are 480 Seconds per email then it takes 8 minutes to handle one email. Advisors can work 60minutes x 90% = 54 minutes per hour. Number of emails per hour = 54 /8 = 6.75 emails per hour.

18 employees x 6.75 emails per hour = 121.5 emails per hour.

So they get 90 new emails per hour. Given that they are dealing with 121.5 emails per hour, they can handle 90 new emails per hour and 31.5 emails per hour of the backlog.

I will leave you to do the maths of how long it takes to clear the backlog.

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