Capacity planning for a service team: workload, Erlang C and interrupt load
For service desk team leads, support and operations managers, and workforce planners who decide how many people a queue needs and how much time is left for project work. Prerequisite: 'Planning staffing, cover and overtime' (staff-hours, shrinkage and rotas); 'Capacity, bottlenecks and flow' is useful background. This course adds the queueing view: offered workload in erlangs for a busy interval, Erlang C to find the agents needed for a waiting-time target, occupancy and why waits grow sharply near full load, splitting a team between interrupt and project work, and presenting a plan with assumptions and triggers. It uses the ITU-D/ITC Teletraffic Engineering Handbook and Google's Site Reliability Engineering book. Working-time rules, contracts and pay are for HR to decide under local law.
- Level
- Intermediate
- Length
- About 94 minutes
- Contents
- 5 lessons · final exam
- Status
- Published · updated 10 Oct 2026
Skills you'll practise
- Calculate the offered workload in erlangs for a busy interval from contact arrivals and average handling time
- Use Erlang C to find how many agents a queue needs to meet a waiting-time target, and state the model's assumptions
- Calculate occupancy and mean waiting time, and explain why waits grow sharply as workload nears the number of agents
- Split team capacity between interrupt work and project work using explicit caps and a ticket rotation
- Present a capacity plan with assumptions, triggers and options for a decision-maker
Course outline
- 1.Calculating the offered workload in erlangs for a busy intervalLesson · 18 min
- 2.Using Erlang C to find how many agents a queue needs to meet a waiting-time targetLesson · 22 min
- 3.Calculating occupancy and mean waiting time, and why waits grow sharply near full loadLesson · 18 min
- 4.Splitting team capacity between interrupt work and project workLesson · 18 min
- 5.Presenting a capacity plan with assumptions, triggers and optionsLesson · 12 min
- 6.Capacity planning for a service team: workload, Erlang C and interrupt load: knowledge checkKnowledge check · 13 questions
- 7.Capacity planning for a service team: workload, Erlang C and interrupt load: practical exerciseKnowledge check · 1 question
- 8.Final exam10 questions · passing it completes the course, so people who already know the material can test out
Sources it draws on
The lessons and questions are written from these references, so learners can go back to the original.
- ITU-D Study Group 2 and ITC: Teletraffic Engineering Handbook (V. B. Iversen, draft 2001-06-20): offered traffic, busy hour, Erlang's C formula and waiting times
- Wikipedia: Erlang (unit), sections on traffic measurement, Erlang C and the limitations of the Erlang formulas
- Google, Site Reliability Engineering, chapter 11: Being On-Call
- Google, Site Reliability Engineering, chapter 29: Dealing with Interrupts
- Google, Site Reliability Engineering, chapter 5: Eliminating Toil
See it with your own jobs and topics
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