WIP limits: why limiting work in progress makes teams faster

WIP limits cap how many items can be in progress at once, for each column or for the whole team.

Ask a busy team to start fewer things and the answer is predictable: we can't afford to slow down. Yet limiting work in progress usually shortens how long each item takes. The reason is arithmetic.

The maths: Little's Law

Little's Law says that average cycle time equals average work in progress divided by average throughput. John Little published a proof of it in 1961.

If a team finishes six items a week and has thirty in progress, each item takes about five weeks on average. Cut work in progress to fifteen with the same throughput, and the average falls to about two and a half weeks.

Nothing about the team's effort changed. Items simply spend less time waiting. Try the numbers in the Little's Law calculator.

When the law holds

Little's Law describes long-run averages in a reasonably stable system. Work should arrive and leave at about the same rate, and you should count all three measures inside the same boundaries.

It does not promise a date for any single item. Use it to understand the system and to set policies.

Why too much WIP hurts in practice

High work in progress brings context switching, more coordination and more work that goes stale before it ships. Each of those can lower throughput, which pushes cycle time up further.

It also hides problems. When there is always something else to work on, a blocked item just sits. Nobody notices until a customer asks where it is.

How to set WIP limits

Make work in progress visible first. Put everything on a kanban board, including the urgent requests that never got a ticket.

Then set a limit slightly below today's level, not an ideal number from a book. When the limit is reached, help finish something before starting something new.

WIP limits and urgent work

Real emergencies need a path. An expedite lane with a limit of one lets urgent work through without breaking the system. If the lane is always full, the problem is upstream.

WIP limits on the shop floor

Factories limit work in progress with kanban cards and small supermarkets between steps. The number of cards caps the stock in the loop. Just-in-time is built on the same idea.

What to measure

Track work in progress, throughput, cycle time and the age of items in progress. These are the four flow metrics in the Kanban Guide.

Over the following weeks, look for cycle times that shorten and become more predictable. If they don't, look at what blocks work. Flow metrics tools can chart all four.

Frequently asked questions