Little’s Law: Understanding the Fundamentals of Queueing Theory [2025]

You’ve read all the books, you’ve checked the web, but you’re still struggling to find the perfect way to make your project more efficient. Meet Little’s Law theorem, one effective way to streamline your project that you might not have heard of yet. (Tools like Basecamp time tracking can also complement such project management strategies, ensuring that team activities are aligned with expected timelines).

With Little’s law formula, you can estimate and turn the queuing processes in your business into a smooth and aligned workflow. It will show you the main system flaws and provide you with insights on how to fix them. In this article, you’ll learn:

• What is Little’s Law?
• How to calculate it?
• How to apply it in your projects.

Understanding Little’s Law in Queue Management

Little’s Law is a practical theory for managing queue systems in methods like Agile and Kanban. Once you get it, you’ve got a key to estimating and improving any queuing process.

Whether you’re managing mobile game development or handling customer lines, Little’s Law is a useful concept to apply.

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Little’s Law Definition and History

📘 Little’s Law was introduced in 1954 by John Little, a professor at MIT. Originally used for analyzing queues in shops, the law applies to anything that can form a queue, including software tasks.

🛠️ Today, it’s used in project management, Kanban boards, software development, manufacturing, and retail operations.

Little’s Law states:
“The average number of customers in a stationary system (L) is equal to the long-term average effective arrival rate (λ) multiplied by the average time (W) that a customer spends in the system.”

🤔 But what does this mean for project management? Let’s simplify the terminology so it’s easier to apply in your workflow:

• 🔁 L = “Customers in a stationary system” → Work in Progress (WIP)
• 📈 λ = “Arrival rate” → Throughput
• ⏱️ W = “Time in the system” → Lead time

✅ With these updated terms, you can now apply Little’s Law to calculate your system’s capacity and improve efficiency.

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Little’s Law Formula

Now, you’ve got the three Little’s law variables. So, what’s the formula? It’s super simple:

L = λ x W

• Work in Progress (L) is the number of items in process in any system.
• Throughput (λ) represents the rate at which items arrive in/out of the system.
• Lead time (W) is the average time one item spends in the system.

Still, seems a bit complicated? Let’s take a look at some real-life examples to add some practical knowledge and visualization to the formula.

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Practical Applications of Little’s Law

🛍️ Let’s apply Little’s Law to a real-world example — a bookstore:

1. 📥 You get 10 visitors per hour.
2. 🕒 Each customer spends about 30 minutes (0.5 hours) browsing before paying and leaving.
3. 📊 So, at any given time, you’ll have 5 customers in the store.

📐 How did we calculate that? Let’s plug in the values using Little’s Law:

L = λ × W = 10 × 0.5 = 5 customers

✅ That tells you there’s no urgent need to hire more staff or expand the space — your current setup handles the load just fine.

📈 But what if 5 customers/hour isn’t enough for your business goals? You run a promo and boost traffic to 20 customers/hour.

L = 20 × 0.5 = 10 customers

Congrats! You’ve doubled in-store activity. But… uh-oh — your single cashier is overwhelmed. Time to rethink resources.

👥 Hiring another seller may help — but it also means double the payroll. If that affects your bottom line, consider marginal revenue strategies to keep profits on track.

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Little’s Law in Project Management

📊 We’ve seen how Little’s Law helps guide decisions in business. But how do you apply it in project management? Easy — because the most popular methods, like Kanban and Agile, are grounded in its principles.

🛠️ In Kanban, the goal is to limit Work in Progress (WIP). High WIP increases lead time, which slows everything down. So, to meet deadlines more easily — reduce your WIP.

📏 To control WIP, you need to know:

• 📥 Task arrival rate (aka throughput)
• ⏱️ Average time each task stays in the system (lead time)

Then, apply the formula:

WIP = Throughput × Lead Time

💡 If you know two of the three values, you can always find the third:

Lead time = WIP / Throughput
Throughput = WIP / Lead time

⚙️ These equations help your team optimize workflows and boost productivity.

🍰 Let’s break it down with a simple example:

• You’re managing a bakery that makes legendary apple pies.
• Five bakers work 8 hours a day and together bake 25 pies daily.

🥧 5 bakers × 8 hours = 25 apple pies

Now, demand is rising! You have two ways to scale up:

• 👨‍🍳 Hire 5 more bakers →

🥧 10 bakers × 8 hours = 50 apple pies

• ⚡ Upgrade your equipment →

🥧 5 bakers × 4 hours = 50 apple pies

🚀 In both cases, you boost throughput — but the second option keeps costs stable by avoiding extra salaries.

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Little’s Law Practice Problems

When applying Little’s Law formula in project estimation, you might run into practical issues. To calculate your project’s WIP correctly, your Kanban system must be in a steady state and all three variables must remain consistent.

Daniel S., one of the early contributors to Kanban development, recommends focusing less on the equation and more on the assumptions that make Little’s Law valid. Once these conditions are in place, your workflow becomes easier to measure and manage.

To ensure your project workflow is predictable and Little’s Law can be applied accurately, your system must meet the following criteria:

• Know your average values: lead time (W), WIP (L), and throughput (λ).
• Keep units consistent. If you measure lead time in weeks, do the same for WIP and throughput.
• Maintain system stability. WIP at the beginning and end of your measurement period should be the same.
• Ensure average arrival and departure rates are equal.

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In Closing

We, at Everhour, hope that now you know how to apply Little’s law in practice, and it’ll help you in your future projects to better:

• Estimate the performance of your project team (learn more about bottom-up estimating here)
• Control project WIP and keep it low to meet deadlines on time
• Explain in practical cases why multitasking is evil
• Meet deadlines
• Make accurate predictions on project workflow and workload.

Enjoyed the article? For more tips, strategies and tools that’ll help you make more informed business decisions and better manage your team, check out these publications next:

Reference:

• Featured image credit: Velog