Erlang Calculator: Estimate the number of people you need

Calculate the number of staff you need beforehand to ensure seamless workforce planning. Get the right number of people on the right tasks at the right time to offer your customers the best experience ever.

Excel Erlang Calculator

  • Time-consuming
  • Manual and complex ✍️
  • Not scalable, (for teams of <5)
  • Requires enabling macros
  • Download for use

Surfboard Erlang Calculator⚡

  • Time-saving
  • Automated and easy
  • Scalable for teams of all sizes 📈
  • No macros installations required
  • Readily available online
per hour
Respond to
of inbounds in
Advanced options
What’s this? The time surfers are paid but are not available to handle calls.
What’s this? The maximum time surfers can spend handling customer interactions and related activities.

Tell us about your inbounds to calculate the required staffing


Your results

Service level
Compute hourly staffing

Adjust the inbound volumes below to calculate hourly staffing


Know more about Erlang calculator

An Erlang calculator is a tool used in telecommunication systems to estimate the resources required to handle a given traffic or workload. It is commonly used in call centres, customer support departments, and other service-oriented environments where there is a need to manage incoming requests or calls.

The Erlang calculator considers the traffic intensity (the average number of arrivals per unit of time), the average call duration, and the desired service level (usually expressed as the percentage of calls answered within a certain time threshold).

Based on these inputs, the calculator estimates the number of surfers required to handle the expected workload. Example of how you can use an Erlang calculator for call centre staffing

Suppose you want to determine how many surfers you need to handle the incoming calls in 1 hour. Historical data that tells you the average number of calls received per hour is 100, and the is 5 minutes (0.083 hours). Your target service level is to is 5 minutes (0.083 hours). Your target service level is to answer at least 80% of calls within 20 seconds.

Input these values and calculate the required number of surfers using an Erlang calculator. 

In this example, the Erlang calculator might tell you that you need 10 surfers to handle the incoming calls during that hour. With 10 surfers available, you can achieve your target service level by answering at least 80% of calls within 20 seconds.

The Erlang C formula is used when a customer is added to a queue because a surfer isn’t available. The customer then stays in the queue until they become available.

The elements in Erlang C formula:

  • Pw = probability of a delay when the customer waits to connect with a surfer, P > 0
  • A =  total traffic (traffic intensity) of the call centre in Erlangs
  • N = number of available call centre resources/agents

The Erlang C formula assumptions:

  • The customer requests follow a Poisson arrival process (number of events over a given period)
  • The number of customers is large.
  • The impact of a single customer has minimal impact on the overall system performance.
  • All customers use the system independently of others.
  • Service times are exponentially distributed.
  • Customers never abandon any service request while waiting for a support surfers.
  • All lost calls are not abandoned but simply delayed.
  • A surfer handles only one customer exclusively for the specified period.
  • The total number of support resources is lower than the number of customers.


The Erlang C formula does not work if customer requests are non-independent or if they're triggered by a common event, such as calling a helpline following a natural disaster. 

The formula usually provides acceptable results only if the number of customers is at least 10 times the number of surfers.

Erlang C is relatively straightforward in application. Here's how it is calculated:

  • Determine the number of call requests per hour.
  • Compute the traffic intensity.
  • Calculate call minutes based on AHT (usually in minutes) per request.
  • Divide call minutes by 60 to compute call hours.
  • Call hours are the traffic intensity, which is expressed in Erlangs.
  • Identify the number of support surfers required to handle the calculated traffic intensity; assume that there's no waiting and every call arrives after a previous call is completed.
  • Calculate the probability of non-zero delay (call waiting) by inserting the above-computed values into the Erlang C formula.
  • Increase the number of service surfers until the desired service level is met.

Manually calculating Erlang C can be cumbersome and time-consuming. Save your time and use Surfboard’s integrated forecasting feature to get your answers in seconds.

Traffic intensity

Traffic intensity is the average number of arrivals (e.g., calls, requests, customers) per unit of time. It is typically measured in Erlangs. The Erlang calculator requires this metric to understand the incoming workload and resource allocation.

Average call duration

This metric represents the average time to handle a single call or transaction. It is usually measured in seconds or minutes. The Erlang calculator uses the average call duration to estimate each surfer's time on a call, influencing the number of resources required to handle the workload.

Service level objective

The service level objective defines the target level of service you want to achieve. It is often expressed as a percentage of calls answered within a certain time threshold. The Erlang calculator considers the service level objective to estimate the surfers needed to meet the desired service level.

Blocking probability

Blocking probability is the possibility that an arriving call or request will be blocked or rejected due to insufficient surfers. It is a measure of how well the system can handle the workload. The Erlang calculator can provide you with an estimate of the blocking probability, which can help you evaluate your performance and make informed decisions about resource allocation.

Number of resources

This metric refers to the available resources in your system that can handle the workload, such as surfers, servers, or lines. It allows finding the right balance between resource availability and service level targets. The Erlang calculator helps you determine the optimal resources required based on the above-mentioned metrics.

Manual calculators

Manual Erlang C calculators require you to input the relevant parameters and perform calculations manually. These calculators typically provide a set of formulas based on Erlang theory, such as the Erlang C formula.

To use a manual Erlang C calculator:

➡️   Input the required parameters.

➡️   Perform the calculations according to the provided Erlang C formulas.

➡️   Interpret the results. 

These calculators are usually available in spreadsheets.

Online calculators

Online Erlang C calculators are web-based tools that automate your calculation process. They are accessible through websites (like Surfboard) and offer a user-friendly interface.

Using an online Erlang C calculator is relatively simple

➡️   Enter the relevant parameters- traffic intensity, average call duration, and service level objective, into the provided fields.

➡️   The calculator then processes the inputs using the underlying Erlang formulas.

➡️   It generates the estimated surfers required to handle the workload.

Online calculators often provide additional features:

✅   Perform "what-if" analyses

✅   Generate reports. 

They are convenient and widely used as they eliminate the need for manual calculations and offer quick and accurate surfer estimation.

Platforms like Surfboard offer forecasting features that allow managers to access historical data and predict inflow up to 12 weeks into the future. Check out how Hypervolt improved staffing accuracy with Surfboard.

Surfboard allows you to build detailed and customisable forecasts with granular insights to streamline call centre staffing in just a few clicks. Schedule a demo to understand how forecasting tools can revamp your support team scheduling.

Start creating schedules based on your forecasts

Get an in-depth product demo to see how Surfboard can help you save time, ensure compliance, and help you hit your service levels


Reduction in time spent in planning your support team


Reduction in time spent scheduling


Improvement in team productivity

Common forecasting questions

Shrinkage in a call centre refers to when surfers are unavailable to handle calls due to various factors such as breaks, meetings, training, and other non-productive activities. Here's how you can calculate shrinkage in a call centre:

  • Determine the total available hours: Start by calculating the total available hours for all surfers during a specific time period. This is typically based on the scheduled shift hours for each surfer.
  • Calculate non-productive hours: Identify and sum up the non-productive hours for all surfers during the same time period. Non-productive hours include breaks, lunches, meetings, training sessions, coaching, and other activities.
  • Calculate shrinkage: Subtract the total non-productive hours from the total available hours to calculate the shrinkage.
  • Shrinkage = Total non-productive hours / Total available hours

To calculate call centre staffing, follow these steps

  1. Gather necessary data such as historical call volume and AHT (Average Handle Time)
  2. Calculate required surfer hours
  3. Calculate the total talk time
  4. Factor in additional time: Consider any additional activities, such as wrap-up time or administrative tasks, and add them to the total talk time to get the total surfer hours needed.
  5. Determine the desired service level
  6. Use Erlang C or other queueing theory formulas
  7. Consider shrinkage factors
  8. Determine staffing levels
  9. Consider coverage requirements

Note - Call centre staffing calculations may vary based on your call centre's specific needs and requirements. Using historical data, queueing theory, and accounting for service level and shrinkage will help you estimate the staffing levels necessary to handle the call volume and efficiently meet customer service targets.

The number of calls a call centre can handle daily can vary significantly depending on factors like the size of the call centre, the number of available surfers, the efficiency of the call-handling process, and the nature of the calls.

Factors like average handle time, service level objectives, and call complexity can also impact the number of calls a call centre can handle. You can use an online Erlang C calculator to estimate calls a call centre can handle daily. 

The Erlang C formula is used for calculating call centre staffing.