Work In Process
It should not be confused with Work in progress, although the terms are often used interchangeably in practice.
The WIP limit
The WIP limit is the deliberate restriction on the number of tasks that can be in progress simultaneously in a phase of the board. It is one of the core mechanisms of the Kanban method for managing the workflow.
Saying that the testing area of a kanban board "has a WIP of 3" means that there cannot be more than three tasks in that phase at the same time. When the limit is reached, no one can add a new task to that column until one of them moves on to the next phase.
Why limit WIP
The WIP limit is not an arbitrary restriction: it is grounded in queueing theory and in Taiichi Ohno's work on the Toyota Production System. The benefits of limiting WIP include:
- Visibility of bottlenecks: when a column reaches its limit and cannot take on more work, the team immediately sees where the problem lies instead of hiding it under new incoming work.
- Reduced lead time: less simultaneous work means each work item gets done sooner.
- Focus: limiting WIP forces the team to finish what has been started before starting something new, reducing the cost of context switching.
Common mistake
Ignoring the WIP limit when the team is "very busy." The temptation to exceed the WIP limit is strongest precisely when there is more urgent work, which is when doing so causes the most damage. Exceeding the limit in moments of pressure hides bottlenecks instead of resolving them, and increases the lead time of all tasks in progress.
See also
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