Why does limiting WIP matters ?

An application of Little’s Law

2 min readJul 13, 2014

For those of you using Scrum, Scrumban or just Kanban, you might be wondering why it matters to limit the Work In Progress (WIP) in a given queue.

Little’s law is defined as:

Reducing the cycle time is of extreme importance when optimizing processes. In the above formula, cycle time can be reduced by either:

reducing WIP (the maximum number of items in progress), OR by
Increasing the throughput

In real-life situations, increasing throughput is only possible up to a certain level and is often limited by the availability of physical resources, for example:

the number of people in a team
the number of CPU’s in a server
the number of hours in a working day
…

It therefore makes sense to decrease the cycle time by reducing the maximum number of items in progress (WIP).

Other benefits of reducing WIP

Besides reducing cycle time, reducing WIP gives a team the following additional benefits:

Reduced task switching and increased focus
Increased feedback: faster feedback on items delivered to customers
Less overload: items don’t pile up in a queue, but transition smoothly from left to right on your planning board
Increased quality: faster feedback in combination with adaptive teams will make the teams produce with a higher level of quality

The main goal of an agile team…

… is to get things done. Reducing WIP will give you the ideal setup to accomplish this goal. It avoids that items are clogging up your queues and, by consequence, avoids that people in the team are facing a backlog too big for them to handle.

In a typical scrum team, the first queue that will clog is the ‘ready for test’ queue. By limiting the WIP, developers aren’t able to push any additional items to the test queue, unless they actively take part in testing themselves to reduce this queue.