Kanban: flow, WIP limits and measurement
The Kanban domain carries the whole of the EXIN Kanban Foundation blueprint. Questions test precise definitions, board mechanics, flow measurement and the reasoning behind limiting work in progress - including small arithmetic on lead time, throughput and WIP.
What the method is
Kanban manages and improves the flow of work using a visual board, explicit policies and limits on work in progress (WIP). It is not a lifecycle model: it prescribes no roles, ceremonies or artefacts, and is layered onto the process a team already runs. Four change principles govern its introduction: start with what you do now; agree to pursue incremental, evolutionary change; respect current roles, responsibilities and job titles; encourage acts of leadership at all levels.
Practices and policies
Six practices: visualise the workflow, limit WIP, manage flow, make policies explicit, implement feedback loops, improve collaboratively and evolve experimentally. Policies are the agreed, visible rules - column definitions of ready and done, WIP limits, classes-of-service handling, blocked-item rules. A rule nobody can see is not a policy.
Board mechanics
Cards move through columns from a backlog, past a commitment point, to a delivery point. WIP limits sit on columns or swimlanes and act as pull signals: a full downstream column stops upstream work rather than absorbing more. Classes of service - expedited, fixed date, standard, intangible - define priority and are modelled explicitly, not by quietly raising limits.
Measuring flow
WIP is work started but not delivered; throughput is items delivered per period; lead time runs from commitment point to delivery point. Little's Law: average lead time = average WIP ÷ average throughput. Flow efficiency = value-adding time ÷ total lead time. A cumulative flow diagram shows band width as WIP, horizontal distance as lead time, vertical rise as throughput. Feedback loops run at set cadences: stand-up, replenishment, delivery planning, service delivery review, operations review, risk review, strategy review. STATIK sequences an introduction: purpose and sources of dissatisfaction, demand and capability, workflow model, classes of service, design, socialise, experiment.
Worked example
A team delivers 5 items a week and holds 20 in progress. Lead time = 20 ÷ 5 = 4 weeks. The customer wants 2 weeks. Throughput is fixed by the bottleneck, so WIP must fall to 2 × 5 = 10; column limits totalling 10 are set and, once the queue drains, lead time falls toward 2 weeks. Adding people or raising limits mid-flow raises WIP and lengthens lead time.
Traps that cost marks
Quoting a lead time without naming the commitment point; treating WIP limits as capacity targets and filling them; assuming Kanban demands new roles or a big-bang rollout; letting expedited items bypass every rule; naming a cadence or a STATIK step without its purpose; confusing throughput (items per period) with WIP (items in progress).