Kanban Social Technologies

The Key to a Kanban Strategy: Understanding WIP Limits

Published on 6 March 2024

Written by Martin Hinshelwood

6 minute read

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One of the most critical components of a successful Kanban strategy is setting Work-In-Progress (WIP) limits. Without WIP limits, you simply do not have a proper Kanban strategy. In this post, we’ll explore the importance of WIP limits, how to determine the right limits for your team, and share some personal experiences and advice to help you optimize your workflow.

Why WIP Limits Matter in Kanban

When you visualize your work on a Kanban board, you’re essentially mapping out the various states or activities that any given piece of work flows through. Each of these states represents a step in the process—whether it’s development, testing, or deployment. But how do you prevent your workflow from becoming overloaded? This is where WIP limits come in.

Setting a WIP limit in each column (or stage) ensures that your team isn’t overwhelmed and that work moves smoothly through the system. It’s about maintaining balance. Too much work at once leads to bottlenecks, whereas too little work means you’re not fully utilizing your team’s capacity.

The Art of Finding the Right WIP Limit 🎨

Figuring out the optimal WIP limit for each stage in your system is both a science and an art. Think of it as finding the “Goldilocks zone”—not too high, not too low, but just right.

I once believed the story of Goldilocks and the Three Bears was universal, but I discovered during a workshop in Romania that they were unfamiliar with it! However, the concept of a “Goldilocks zone” resonated well when I explained it using planetary physics.

In planetary terms, the Goldilocks zone is where water isn’t frozen or boiling, making life possible. Similarly, in Kanban, the right WIP limit is the sweet spot where work flows smoothly without getting stuck or overwhelming the system.

Setting WIP Limits at Each Stage

WIP limits aren’t just for the overall system—they need to be set for each individual stage. These individual WIP limits will also inform the overall WIP limit for your entire system.

Ideal WIP Limit: Striving for Perfection

In an ideal world, the optimal WIP limit is one—meaning single-piece flow, where only one item is being worked on at a time. This ensures maximum efficiency and the fastest possible delivery of work. Sounds perfect, right? But here’s the thing: the world isn’t perfect.

The coin game exercise illustrates this well. If you haven’t tried it with your team, I highly recommend it. You take a group of people and give them 20 coins. Each person must flip all the coins to heads, then tails, before passing them to the next person. If you do this in batches of 20, only one person is working at any given time, and the rest are waiting.

But when you reduce the batch size to one coin at a time, everyone is working simultaneously, resulting in faster delivery for all coins.

💡 Key takeaway: The smaller your batch size, the quicker you can deliver individual pieces of work. But remember, we’re not flipping coins in real life. We’re dealing with complex tasks like coding, designing, and customer feedback—so things get a little more complicated.

Balancing Real-World Complexity 🌍

In the real world, work isn’t linear. We’re not simply flipping coins. We’re solving problems, writing code, waiting for feedback, or managing customer requests. This complexity means we need to carefully determine the most optimal WIP limit for each stage in our process.

How to Identify the Right WIP Limit

Start with experimentation: There is no magic formula. Begin by setting an initial WIP limit and observe how your system behaves.
Constrain work to create slack: Setting WIP limits slightly below your team’s full capacity creates slack in the system, allowing you to identify bottlenecks and opportunities for improvement.
Adjust based on feedback: If your WIP limit is too high, you’ll struggle to spot problems because the system never feels constrained. If it’s too low, you’ll notice inefficiencies from too much idle time. Adjust accordingly.

Workshop Insights: Discussions on WIP Limits

During workshops, one of the most fascinating discussions is always about whether to increase or decrease WIP limits. Participants quickly realize that raising the limit might allow more work to pile up, but it also puts pressure on other parts of the system. These discussions are invaluable because they help teams visualize the impact of WIP limits and make more informed decisions about how their system functions.

The Goal of Kanban: Better Conversations, Better Systems

The beauty of a Kanban strategy lies in how it helps everyone in the system understand the work being done. Visualizing WIP limits opens up more rational and meaningful conversations about how the system works and how it can be improved.

Tips for Setting WIP Limits in Your Team

If you’re unsure where to start, here’s my advice:

Start small: Pick an initial WIP limit and monitor its impact.
Make adjustments: Increase the limit if it’s too small, or reduce it if it’s too high.
Use the “one less rule”: If you’re really stuck, a simple starting point is to set the WIP limit to one less than the number of people performing that activity. For example, if you have four people working on a task, set the WIP limit to three.

These rules are not set in stone—they’re just a guide to help you get started.

Implementing Kanban in a Scrum Team 🛠️

While Kanban and Scrum are often seen as separate, they can complement each other beautifully. If you’re using Scrum, bringing in flow metrics from Kanban can greatly enhance your process. For Scrum teams, we always recommend integrating Kanban practices to visualize work and identify bottlenecks early.

World-Class Kanban Training

If you’re struggling to implement a Kanban strategy, or if you’d like to optimize your current process, we offer world-class Kanban training and coaching through Pro Kanban. We can help your team fine-tune their WIP limits and ensure you’re operating at maximum efficiency.

👉 Need Help? Reach out to us for guidance on implementing Kanban in your team, or explore our Kanban classes from Scrum.org. Together, we can find the right balance for your workflow.

Conclusion: Start Experimenting with WIP Limits Today

WIP limits are crucial for any Kanban system. While the “perfect” WIP limit might be one, real-world complexity means you’ll need to experiment and adjust based on your team’s capacity and workflow. Start with small experiments, encourage open discussions, and watch how it transforms your team’s productivity and collaboration.

🔍 Remember:

WIP limits are an essential part of your Kanban strategy.
Set limits for each stage, not just the overall system.
Experiment and adjust as needed to find the Goldilocks zone for your team.

With the right approach, you’ll find that WIP limits not only improve flow but also foster better conversations and collaboration within your team.

One of the key components of creating a Kanban strategy is WIP limits. If you don’t have WIP limits, it’s definitely not a Kanban strategy that you have. So when you visualise your work, when you do that workshop where you figure out what are the columns, the states, the activities that happen for any piece of work that flows through our system, and you create those columns, you’re going to have to decide what your WIP limit is in each of those areas. Coming up with a WIP limit is a little bit of an art, right? It’s like coming up with what’s the Goldilocks zone for this particular activity.

I actually found out that I really fundamentally thought that Goldilocks and the Three Bears was a completely ubiquitous story. But I was working recently with a group in Romania, and they don’t have Goldilocks and the Three Bears as a bedtime story. It’s not a thing. So kind of what we’re talking about, and actually this was the bit that resonated the best for them, was think of what they describe as the Goldilocks zone in planetary physics. I know I’m sounding like a nutball here, right? But bear with me.

In planets, when they talk about planets being in the Goldilocks zone, they mean it’s between water freezing and water boiling, right? So you can have life when there’s water, but you can’t have life when it’s steam. In general, that’s where they—yes, I know that’s possible—but let’s say you’ve got that zone. If the water’s frozen, it’s probably very difficult to have life. If the water’s steam, then it’s very difficult to have life. So what is the zone within which it’s just right? That’s the Goldilocks zone. You can go look up the story, the fable, later.

The idea is that we need to figure out not just our WIP limit for the whole system, but our WIP limit for individual stages in the system. The WIP limit for the individual stages, if we create individual stages, will probably inform the WIP limit for the overall system, right? Because you just add them up, and that’s the WIP limit for the whole system.

So, the ideal WIP limit, right? There is an ideal WIP limit. If everything is perfect, the ideal WIP limit is one. The most optimal WIP limit in flow is one single piece flow, right? But that only works when our system is perfect, when it operates exactly like we expect, in the timing we expect, when all of those things are absolutely perfect.

The WIP limit is one. The thing I usually use to visualise that is I do a version of the coin game with teams. If you’ve not done the coin game, it’s a great exercise where you give a group of people 20 coins. They flip them all to heads, and then it’s a batch size exercise, right? So they flip them all to heads, and then they have to flip them all to tails, pass to the next person, and they have to flip them all to tails, pass them to the next person. So you’ve got this simulation of a production line, right? Something happens in this stage, the next stage happens, something happens there, next stage.

In an ideal world, you just want one flip, the coin, move it on, flip the coin, move it on, flip the coin, move it on, and you’ll have the maximum number of coins going in action at any point in time. Does that make sense? Right? If you’ve got a batch size of 20 and you’ve got 20 coins and you’ve got 10 people in a row, you’ve got one person working and nine people waiting all the time, the whole time. If you do a batch size of one, you’ve got 10 people working, and you’ll get the fastest delivery of the first unit of work and the fastest delivery of all the units of work.

Okay, but the world isn’t made up of flipping coins, right? We’re not—that’s not what we’re doing all day. We are writing code, we’re solving problems, we’re painting pictures, we’re waiting on customers to reply. There’s all sorts of things that make what we do a nonlinear thing, not a thing that just happens at once. So you’re going to have to figure out for each of those columns what the most optimal WIP limit is based on your ability to keep things moving and the need to identify when there’s problems.

If we make the WIP limit 100 in every column, it’s going to be difficult to identify problems because we’ll maybe never hit it. We’ll never hit the WIP limit. We deliberately want to constrain the work to slightly less than we can do so that we create slack in the system that enables us to see more of what’s going on, ask more interesting questions, and figure out do we need to increase this or reduce this one. Those are the types of discussions that we want to have.

Whenever we run workshops where we run simulations around this, that’s the kind of conversations that people have in the groups. Who should we create the WIP limit bigger? Yeah, but if we create the WIP limit bigger, then there’ll be more stuff in here, and there’ll be more pressure on this part of the system. The people in the groups are then able to visualise those things and see the impact of those things, which is the whole point of a Kanban strategy—that everybody in the system understands the system that you’ve created better, and it allows them all to have more rational, more interesting conversations about how the system goes together and how we might change it in order to improve it or attempt to improve it, and then the impact of those improvements. You’re able to monitor them.

That is really picking WIP limits. Just make up some numbers at the start, pick stuff, and see what works. Increase them if they’re too small, make them smaller if they’re too big, and figure out where that optimal level is. If you’re really searching for Martin, what would you recommend as our WIP limit? I would say in any stage, as a starting point, if you have to have a Martin says we should do it this way, if you have to have that, then pick one less than the number of people that you have performing an activity in that area. So if you have four people, pick three as your WIP limit and see how you go.

If you’re struggling to create WIP limits so that you can see what’s going on in your system, then we can help you. We provide world-class Kanban training from Pro Kan, as well as consulting and coaching for teams trying to implement Kanban strategy. If you’re a Scrum team, then we always recommend bringing in flow metrics as a complimentary practice and also have Kanban classes from Scrum.org.

Strategy Operational Practices Practical Techniques and Tooling Flow Efficiency Agile Frameworks Software Development Lean Thinking Agile Project Management Pragmatic Thinking Throughput

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