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 without using the Erlang Calculator.


Call Centre Helper

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

Use an Erlang Calculator
(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 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

You can just plug your numbers in there.

Planning & Control

Erlang is the best way to calculate it
<p>Srikanth - 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.</p>
<p>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.</p>
<p>@ 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

Erlang Calculator
Not sure why you want to do it without an Erlang calcuator?
There are a couple of free excel based Erlang calculators that could do the job for you here



<p>@ 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!!!


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

Now in order to come up with the actual number of FTEs required to cater the need.

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

I posted the below in response to a similar question, may be of some help


I've always regarded this as two seperate calclulations. 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.

One simple way is just to tally up the total calls each month, multiply by 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 allowed 12% for breaks, etc and then a further 8% for Admin (121's meetings, etc) These were all cumulative figs - 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). After baking in a hot oven for, what you will have is your overall headcount requirement (albeit just based on 1 month - but rinse and 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

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

@ 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 sicnkess 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 wouldnt count breaks for this time, so it would be cumulative, but a day of sickness or holiday typically wont result in their 121 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 k out.

Resource Planner/Infrastructure Analyst

Lloyds Banking Group

Hi Kevin,

Your points are valid, but if I've read you right that's not actually what I'm doing. My calcs are based on assuming that (just using fictional figs) 10% of staff are on hol and on top of that a further 5% are off sick. Then of those who are in there is an additional shrinkage to be added.

You raise a fair point in that the actual calcs 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.

Can anyone help me with my FTE math breakdown?


Did anybody ever came across the Term "Working Shrinkage" in a Call centre environment, if yes what would the Definition/Calculation be?

Thanks, Lino

Capacity Planning Specialist

Calculating Shrinkage
This article should help you with

How to calculate contact centre shrinkage.


For this below values what will be the Required Actual number of agents, Please help

Volume Actual: 4

AHT Actual : 404

Delay Actual : 12

Required Act: ?

Service Level : 80

Shrinkage PCT : 20.5

Required Actual is the Staff Group's Actual Required without Staff Adjustments and Unproductive

The number of staff required to handle the actual volume of calls.

Vol Act :Actual Contacts Offered.The actual number of offered contacts reported by the ACD.

Req Act should 3.02, Please help with the logic

Please help ,Please help, it is very urgent to me.

Try here:

You'll then need to factor your shrinkage




Thanks for your suggestion, I have tried that excel many times, but it is always giving a difference of 5 or 4 and 1 for smaller groups, Please help me in that logic, I was stuck up with this since one month.

I want how the calculation happens, I tried different ErlangC Excels but it is vain.


Please @applebyd, My tool is calculating and giving the result as 3.02, I tried that excel, but it is giving other value. Please let me know how to achieve this. some sample data











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!




i am preparing an analysis study on call center 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 -->

=AgentsFTE(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 Dannis,

Thanks a lot for your help :)Kindly help me with the templates if possible. I'm a begineer. Thanks in advance.

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

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. Stay tuned and we will add in a link when it is available.

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




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

- Editor]

Need forecasting help
I have basic information and nothing more but I am being asked to provide some detail as to a recommendation on staff needed. Here is the information I have:

Forecasted Monthly Membership (xxxxxx)(variable)
Forecasted Call Factor (0.032)
Forecast AHT 400 seconds
Forecast Occupancy 85%
Forecasted Shrink 35%

I have no past data to use, so I need to recommend a ball park figure on staffing need per day. Service level is 85%/60 sec.

Any ideas would be appreciated.


Call Centre Helper

It's easy with an Erlang Calculator
This is quite easy. 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.

Want to know
Calls is 5000
Aht is 55 seconds
Occupancy is 80%

What is the fte required pls help me for the calculation


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 shrinkages call centres usually take into account will include screen breaks, training, coaching, 121s and team meetings. A shrinkage of 30-40% (71-83 agents required) is common in my experience but depends what type of call centre it is.

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