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.

Note

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.