Kanban guide · Flow and metrics
Blocker Clustering: Find the Root Causes of Delays
Every team gets blocked: waiting for approvals, other teams, environments or information. Blocker clustering is a simple technique, popularised in the Kanban community by Klaus Leopold and Troy Magennis, for turning those daily frustrations into data you can act on.
Key takeaways
- Record every blocker with its reason and duration.
- Cluster similar blockers and measure their cost in blocked days.
- Fix the biggest clusters first.
How it works
- Mark blockers on cards as soon as an item can't progress, with a short reason and the start date.
- Record when the blocker is removed, so you know how long it lasted.
- Collect blocker records over a few weeks.
- Cluster them in a workshop: group similar blockers into categories, such as waiting for test environments, unclear requirements or external approvals.
- Measure each cluster: how many blockers and how many blocked days.
- Act on the biggest clusters with targeted improvements.
Example clusters
| Cluster | Count | Blocked days | Possible action |
|---|---|---|---|
| Waiting for test environment | 14 | 38 | Automate environment set-up |
| Unclear requirements | 9 | 21 | Better refinement and acceptance criteria |
| External approval | 6 | 30 | Agree service levels with the approving team |
Illustrative numbers only.
Internal vs external blockers
Separate blockers your team can fix from those that need other teams or leaders. Internal clusters can be tackled in the next retrospective; external clusters need data to support a conversation with the other party.
Tips
- Make marking blockers quick and blame-free.
- Review clusters monthly.
- Track whether blocked days fall after each improvement.
- Combine with a cumulative flow diagram to see the effect on flow.
Free templates for this topic
Frequently asked questions
How long should we collect data before blocker clustering?
A few weeks is often enough to see patterns. Continue collecting so you can measure the effect of improvements.
Who should take part in a blocker clustering session?
The team, plus anyone who can help resolve external blockers.
What is blocker clustering?
Blocker clustering is a technique for collecting records of blocked work over time, grouping them by cause and tackling the clusters that cause the most delay.
Who created blocker clustering?
The technique was popularised in the Kanban community by Klaus Leopold and Troy Magennis.
What counts as a blocker in blocker clustering?
A blocker is anything that stops a work item progressing, such as waiting for an external approval, missing information or a broken environment.
How do you record blockers on a Kanban board for blocker clustering?
Attach a blocker marker to the card with a short reason and the date it became blocked, and note the date it was cleared. Keep the records when the blocker is removed.
How do you group blockers in blocker clustering?
Lay out the blocker records and sort similar causes together, such as "external approval" or "test environment". Then total the count and days blocked for each cluster.
Does blocker clustering work for impediments as well as blockers?
Yes. The terms mean much the same: "impediment" is common in Scrum, while Kanban teams usually say blocker, so Scrum teams can cluster impediments the same way.
How do you prioritise the results of blocker clustering?
Rank the clusters by total days lost, not just frequency, and consider how easy each is to fix. A few clusters usually account for most of the delay.
What tools help with blocker clustering?
Sticky notes on a wall are enough. Digital boards can export blocked-time data, and a fishbone diagram helps find the root causes of a large cluster.
How does blocker clustering improve flow?
Removing the most common causes of blocking cuts waiting time, which improves flow efficiency and shortens cycle time.