Mastering call centre staffing with Erlang C

How to use Erlang C in a call centre
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Picture of Natasha Ratanshi-Stein

Natasha Ratanshi-Stein , Founder & CEO

Managing a call centre comes with its own set of hurdles: high turnover, maintaining quality service, keeping up with tech advancements, and controlling call volumes. Add the need for speedy, personalised service, and the complexity mounts. Tackling these challenges and boosting customer satisfaction and operational efficiency demands a modern, data-driven strategy.

That’s where Erlang C comes in: a robust tool for forecasting staffing needs. It enables informed decision-making, aligning staffing precisely with service demands to maximise efficiency and elevate customer satisfaction.

What Is Erlang C?

Erlang C is a key mathematical formula in telecommunications and call centre operations, designed to forecast call waiting times and optimise staffing for effective call volume management. Originating in 1917, from A.K. Erlang’s early work in traffic engineering, Erlang C plays a crucial role in efficiently deploying call centre resources, ensuring prompt and effective service that boosts customer satisfaction and operational efficiency.

In contrast to Erlang B, which addresses call blocking in circuit-switched networks, Erlang C focuses on managing queues and scheduling agents to minimise wait times and improve service efficiency. This distinction makes Erlang C invaluable for call centres aiming to enhance service delivery and operational performance by optimising wait times and resource use.

The importance of Erlang C in workforce management

In workforce management (WFM), Erlang C acts as a key tool for fine-tuning staff levels in call centres. It helps forecast the number of agents needed to manage expected call volumes, ensuring quick and efficient customer service. 

The advantages of using Erlang C are significant. It allows for accurate staffing, matching workforce size to demand without overspending, which is crucial for your cost efficiency and service quality. It also reduces your customer wait times, enhancing the service experience and potentially boosting loyalty. Moreover, Erlang C aids in strategic workforce planning, helping you anticipate needs for peak times- and adjust schedules accordingly.

Beyond just number crunching, it’s a strategic tool for precise planning and agile response, enabling call centres to surpass customer expectations and stay competitive. Its role in promoting continuous improvement and integrating technology highlights its lasting impact on workforce management’s future.

How do I calculate Erlang C?

You’ve read a lot about Erlang C, but how is it calculated? Erlang C calculation requires several key parameters:

  • Traffic intensity- the number of calls received in a given period
  • Average call duration- the average number of minutes it takes your agents to handle a request
  • Service level agreement- the target level of service you want to achieve

Using these parameters, the Erlang C formula tells you how many agents you’ll need, based on the given data, to meet your SLAs. Note that there are a few assumptions when using Erlang C. This calculation assumes that calls aren’t lost while customers wait for an agent to respond, and that customer requests are independent of each other.Understanding and applying the Erlang C formula can be challenging due to its mathematical complexity. Try avoiding a headache and use Surfboard’s free online calculator to experience firsthand the simplicity and effectiveness of Erlang C calculations.

Implementing Erlang C in your call centre

Implementing Erlang C into your call centre’s staffing practices can transform the efficiency and effectiveness of your customer service operations. Practical tips for integrating Erlang C include:

Accurate measurement

With Erlang C’s utility coming from its reliance on data, it’s important to ensure the data you’re entering is right. Using workforce management software, you’re able to track these parameters and ensure that you can make accurate Erlang C calculations. Surfboard’s team insights tracker combines simplicity with precision, giving you the most powerful data to inform your decisions. You’ll also be able to track other metrics which come into play in Erlang C calculations, like shrinkage or occupancy, to ensure that your staffing estimates reflect real-life scenarios.

Regular review and adjustment

Implement a continuous improvement process that regularly reviews staffing predictions versus actual outcomes. Use these insights to refine your Erlang C parameters, ensuring your staffing practices evolve in line with changing call patterns and service objectives.

Balancing staff flexibility

Develop flexible staffing strategies that allow for quick adjustments. This flexibility is key to responding to unforeseen variances in call volume, ensuring you maintain service levels without excessive overstaffing.

Success stories using Erlang C

Emergency response units like the 911 service in the United States have employed Erlang C models to calibrate their staffing requirements for call operators. This ensures enough operators are always on hand to address incoming calls promptly. By leveraging Erlang C, these critical services significantly reduce the likelihood of callers waiting on hold during emergencies, where every second counts.

Erlang C not only serves as a tool for predicting call volume and staffing needs but also embodies a strategic approach to operational excellence in emergency call centres. Through its application, these services can maintain the delicate balance between operational efficiency and minimising response times.

Common mistakes and misconceptions

A key pitfall when applying the Erlang C model is ignoring call volume fluctuations and varying handling times, leading to inflexible staffing that can’t match real-time needs. This often causes overstaffing in quiet times and understaffing during spikes, hitting costs and service quality hard. Another oversight is not regularly updating the model with fresh call data, crucial for boosting its accuracy and reliability. Constantly refining Erlang C with actual performance data keeps it sharp, optimising staffing to boost efficiency and customer satisfaction.

To navigate these challenges, it’s crucial to integrate dynamic data analysis and real-time monitoring into the Erlang C implementation process. Erlang C in WFM uses real-time data analytics and can provide the flexibility needed to adjust staffing levels as demand changes.

Data-driven planning using Erlang C enables your business to meet the dual objectives of cost efficiency and superior customer service. Boosted with the insights through advanced workforce management solutions like Surfboard, practical implementation of Erlang C equips you with the tools plan according to forecasted data, and meet your SLAs.

By leveraging Surfboard’s analytics and user-friendly interface, businesses can integrate Erlang C into their staffing practices, ensuring that the right number of agents are available at the right times to meet customer needs without incurring unnecessary costs.


What is Erlang C?

Erlang C is a pivotal mathematical model for call centres, predicting queue times, staffing needs, and performance metrics. It’s key to resource management and boosting call centre efficiency. Developed by Danish mathematician A.K. Erlang, this model extends the Erlang B formula, offering a solid foundation for operational excellence.

What is Erlang in WFM?

In Workforce Management (WFM), “Erlang” is crucial for calculating staff needs in contact centres. Specifically, the Erlang C model forecasts the required number of agents to meet call volumes within targeted service levels and answer times. This ensures:

  • Optimal staffing: Balancing agent availability with service demands, minimising costs.
  • Reduced wait times: Aligning staffing to demand reduces customer wait times, boosting satisfaction.
  • Efficient scheduling: Erlang helps tailor shifts to demand, enhancing service and cost-efficiency.

Erlang-based WFM tools enable data-driven staffing, aligning operational efficiency with customer service goals for improved contact centre performance.

What is Erlang B and C?

Erlang B zeroes in on blocking probabilities in queue-less systems, perfect for circuit-switched networks where calls are instantly connected or dropped. It calculates how many lines are needed to hit specific blocking rates with a given traffic load.

Erlang C, tailored for queue-based systems like call centres, estimates wait times and required staff to meet call volumes and service targets. Unlike Erlang B, it assumes queues are a given, optimising call centre operations for a fine balance between customer satisfaction and staffing efficiency.

How do I calculate Erlang C?

Calculating Erlang C involves key parameters: traffic intensity (call volume), average call duration, and your service level agreement (SLA) goals. This formula determines the necessary agent count to meet SLAs, assuming no call loss during wait times and that each customer request is independent. Given its mathematical complexity, leveraging tools like Surfboard’s free online Erlang calculator simplifies Erlang C application, offering an effective way to streamline staffing based on precise, data-driven insights.

What is an Erlang in telecoms?

In telecoms, an “Erlang” measures traffic volume or load across telecom systems. Named for A.K. Erlang, a Danish mathematician who founded traffic engineering, it’s essential for telecom capacity management. One Erlang equals one hour of traffic on a channel. For example, a line used for 30 minutes generates 0.5 Erlangs. Two channels used for 30 minutes each within an hour also equal 1 Erlang, demonstrating its role in quantifying and planning network traffic efficiently.