What is Lean Six Sigma

Guide: Fundamentals of Lean Six Sigma

Lean Six Sigma is a powerful operational improvement methodology that synergizes the efficiency-focused Lean principles with the quality-centric Six Sigma approach. Originating from the best practices of Japanese manufacturing, particularly Toyota’s Production System, Lean emphasizes creating more value for customers using fewer resources. It involves identifying and streamlining value-creating steps, ensuring smooth process flow, and adopting a customer-centric production approach.

On the other hand, Six Sigma, developed by Motorola, employs a data-driven methodology to minimize defects and reduce process variability. It leverages statistical tools and a structured DMAIC (Define, Measure, Analyze, Improve, Control) process for continuous quality improvement. The fusion of these methodologies into Lean Six Sigma offers a comprehensive toolkit for enhancing operational efficiency and product quality, fostering a culture of continuous improvement and excellence in organizations.

Table of Contents

What is Lean Six Sigma?

Lean Six Sigma is an operational improvement methodology that combines two separate improvement methods, Lean and Six Sigma. To understand the combination of Lean and Six Sigma in-depth, it is important to understand each of these components separately before understanding how they integrate.

Lean: The Pursuit of Efficiency

Lean is about maximizing value for the customer while minimizing waste. It is as much of a philosophy as it is a methodology. Lean has roots in Japanese manufacturing, particularly with Toyota and the Toyota Production System (TPS). The focus of Lean is on creating more value for customers using fewer resources. 

The key principles of Lean are:

Identifying Value: The first step in Lean is to specify value from the standpoint of the end customer. This ensures that every process step adds something the customer is willing to pay for.

Mapping the Value Stream: In Lean, the value stream is the entire lifecycle of a product or service, from raw materials to the end customer. Mapping this out helps identify and eliminate non-value-added steps.

Creating Flow: Once the waste is removed, the steps that create value should occur in a tight sequence to ensure a smooth flow of materials and information.

Establishing Pull: Instead of pushing products to market, Lean suggests producing only what customers need and when they need it. This reduces inventory and waiting time.

Pursuing Perfection: Lean is an ongoing process of continuous improvement. Companies strive to perfect their processes by continuously identifying and eliminating waste.

The Principles of Lean

Six Sigma: The Quest for Quality

Six Sigma offers a more data-driven approach. It was developed by Motorola in the 1980s as a way to systematically improve the quality of their products. The core of Six Sigma lies in understanding and reducing variability in processes, which can lead to defects. Key elements include:

Focus on Customer Requirements: Six Sigma emphasizes understanding and meeting customer needs and specifications.

Use of Statistical Tools: Six Sigma relies heavily on statistical methods to analyze and improve processes. It aims to make processes more predictable and reduce variability.

Process Improvement Expertise: Six Sigma uses a belt system (Yellow, Green, Black, Master Black Belt) to signify levels of training and expertise in these techniques.

DMAIC Methodology: This stands for Define, Measure, Analyze, Improve, and Control. It’s a data-driven quality strategy used to improve processes.

Reduction of Defects: The ultimate goal of Six Sigma is to reduce the number of defects in a process to a statistically insignificant level, typically aiming for no more than 3.4 defects per million opportunities.

Six Sigma Principles

Combining Lean and Six Sigma

Combining Lean and Six Sigma creates a powerful approach to continuous improvement known as Lean Six Sigma, combining the best elements of both methodologies to achieve superior process improvement.


Lean, with its focus on the speed and efficiency of processes, excels at removing waste and improving flow. Whereas, Six Sigma, is focused on ensuring precision and accuracy, aiming to reduce process variation and defect.

Combining these two:

  1. Efficiency Meets Quality: Lean’s speed and waste reduction complement Six Sigma’s focus on quality and precision. This leads to processes that are not only faster and leaner but also consistent and of high quality.

  2. Broader Toolkit: Improvement practitioners have access to a wider range of tools and techniques from both Lean and Six Sigma, allowing for more versatile and effective solutions to a variety of problems.

  3. Cultural Transformation: Lean Six Sigma fosters a culture of continuous improvement and quality consciousness, which can lead to significant long-term benefits for a business.

The Five Principles of Lean Six Sigma


The integration of Lean and Six Sigma gives rise to five key principles that guide this methodology:

Define Value: The key principle of Lean Six Sigma is the understanding of what constitutes value from the customer’s perspective. This principle emphasizes that all process improvements should be aligned with customer needs and preferences. By focusing on what the customer values, businesses can ensure they are not using resources on what is considered waste.

Map the Value Stream: This involves identifying every step in a process and evaluating it for its contribution to value creation. This ‘value stream mapping’ helps in visualizing inefficiencies and bottlenecks. Steps that do not add value (non-value-added activities) are prime targets for elimination or improvement. This might include redundant processes, unnecessary movements, waiting times, overproduction, or defects.

Create Flow: Once waste is removed, the next goal is to ensure that the remaining, value-adding steps flow smoothly. This means reorganizing work sequences, optimizing workspaces, and employing techniques like Just-In-Time (JIT) production to ensure that work progresses with minimal stops and starts. Smooth flow reduces cycle times and increases responsiveness to customer demands.

Establish Pull: Instead of producing based on forecasts, Lean Six Sigma advocates producing in response to actual demand. This ‘pull’ approach reduces inventory levels and minimizes waste associated with overproduction. It ensures that resources are allocated only when there is a real customer need, thereby aligning production closely with market demand.

Pursue Perfection: Continuous improvement is a fundamental aspect of Lean Six Sigma. The journey towards perfection is an ongoing process of identifying and eliminating waste, reducing process variation, and continually striving to meet and exceed customer expectations. This principle encourages a culture where employees are always looking for ways to improve processes and quality.

The DMAIC Process in Lean Six Sigma

You can get an in-depth understanding of DMAIC with our DMAIC guide. However, we will give you a brief overview in this introduction guide.


The Define phase of DMAIC sets the foundations for the project. It involves clearly defining the problem and the goal of the project; it will also clarify the scope and set clear objectives for the success of the project.

This phase will include identifying the customers, both internal and external, and their requirements, forming a project team, and creating a project charter.


Once the define phase is complete, the next step is the measure phase, which focuses on collecting data to understand the current state of the process and is referred to as a baseline for comparison.

This stage will include identifying Key Performance Indicators (KPIs), mapping the current process to understand its flow, and collecting the necessary data to understand the process. In this stage, the accuracy and reliability of the data are important.


Following the data collection (measure) phase, the next step is to analyze the data to identify the root causes of the problem.

This step involves selecting the most suitable statistical and analysis tools, such as fishbone diagrams, Pareto analysis, and hypothesis testing. This is done to analyze the data and identify where and why defects or inefficiencies are happening.


Once the data has been analyzed and the root cause of the problem has been identified, the next step is to make improvements to solve the problem. This will involve developing and implementing solutions that address the root causes.

Actions in this step may involve redesigning and mapping out the process, implementing new procedures, and/or conducting pilot tests to evaluate the effectiveness of the proposed solutions. This phase of DMAIC will require creativity, innovation, and often change management skills.


The final phase of DMAIC is control; this stage of the process is all about controlling and sustaining the improvements that have been made. This step involves putting in place control mechanisms such as process monitoring, ongoing data collection and control, and response plans for potential future deviations. The aim is to maintain the gain achieved and ensure the process continuously improves.

Lean Six Sigma Roles and Responsibilities

The belt-based system in Lean Six Sigma, inspired by martial arts, each color refers to different levels of expertise and responsibility. This system not only facilitates a structured approach to training and skill development but also helps in the effective implementation and management of Lean Six Sigma projects within an organization.

White Belt

A practitioner qualified to a White belt will have introductory knowledge and a basic understanding of Lean Six Sigma Principles


  • Gains a basic understanding of Lean Six Sigma principles.
  • Learns about the basics of the DMAIC process (Define, Measure, Analyze, Improve, Control).
  • Can participate in problem-solving teams and support Lean Six Sigma projects in a limited capacity.
  • Often, White Belts help with change management and can work on localized team-based improvements.

Application: White Belts are typically employees who need an awareness of Lean Six Sigma for organizational culture and participation in improvement initiatives.

Yellow Belt

A practitioner qualified to a Yellow belt will have a fundamental level of knowledge of Lean Six Sigma and a more detailed understanding of the Lean Six Sigma process.


  • Has more detailed knowledge of the Lean Six Sigma process.
  • Participates in project teams, often assisting with data collection and analysis.
  • Can lead small-scale improvement projects or assist Green and Black Belts in larger projects.
  • Understands basic problem-solving tools like Pareto charts, cause-and-effect diagrams, and basic statistical tools.

Application: Yellow Belts are valuable in supporting process improvement projects and often form a bridge between the process improvement team and the rest of the workforce.

Green Belt

A practitioner qualified to a Green belt will have an intermediate level of knowledge of Lean Six Sigma a more detailed understanding of the Lean Six Sigma process and the ability to run small projects.


  • Leads smaller Lean Six Sigma projects or plays a significant role in larger projects led by Black Belts.
  • Possesses a deeper understanding of the DMAIC process and is skilled in analyzing and solving quality problems.
  • Trained in a wider array of statistical techniques and tools than Yellow Belts.
  • Responsible for gathering data, process mapping, and driving small-scale improvements.

Application: Green Belts are often employed in roles where they can leverage their Lean Six Sigma expertise while maintaining their regular job functions.

Black Belt

A practitioner qualified to a Black belt will have an advanced level of knowledge of Lean Six Sigma a strong understanding of the Lean Six Sigma process and the ability to run larger projects and provide support to Green belts and Yellow belts.


  • Highly skilled in the Lean Six Sigma methodology.
  • Leads complex, cross-functional projects and is responsible for managing the project from inception to completion.
  • Provides statistical analysis and is proficient in advanced quality tools and techniques.
  • Mentors Green and Yellow Belts and contributes to strategic decision-making in process improvement.
  • Application: Black Belts usually serve in full-time roles focused on continuous improvement and process excellence within the organization.

Master Black Belt

A practitioner qualified to a Master Black belt will have an expert/strategic level of knowledge of Lean Six Sigma an in-depth understanding of the Lean Six Sigma process and the ability to run larger projects and train, mentor and coach Black belts and Green belts.


  • Has extensive experience and deep knowledge of Lean Six Sigma.
  • Oversees the strategic implementation of Lean Six Sigma within an organization.
  • Responsible for training, coaching, and mentoring Black Belts and Green Belts.
  • Plays a key role in policy and strategy development for Lean Six Sigma.
  • Often involved in the high-level business strategy and ensures that Lean Six Sigma initiatives align with organizational goals.

Application: Master Black Belts are top-tier professionals, often found in executive or senior leadership roles, driving continuous improvement at a strategic level.


Lean Six Sigma stands as a testament to the power of combining efficiency and quality in operational processes. By integrating Lean’s waste-reducing, value-adding principles with Six Sigma’s stringent quality controls and data-driven approach, organizations can achieve a remarkable transformation in their operational performance.

The methodology’s belt-based system of expertise, ranging from White Belt to Master Black Belt, ensures a structured development and application of skills across various organizational levels. This leads to a deep-rooted culture of continuous improvement, where every employee plays a role in optimizing processes and enhancing quality. Lean Six Sigma, therefore, is not just a methodology but a strategic tool that empowers organizations to reach new heights of efficiency and excellence, aligning closely with customer needs and market demands.


A: Lean Six Sigma is a methodology that combines the principles of Lean Manufacturing and Six Sigma to improve process efficiency, quality, and customer satisfaction. It focuses on eliminating waste, reducing process variation, and driving continuous improvement

A: While traditional Six Sigma focuses primarily on reducing process variation and defects, Lean Six Sigma combines the statistical rigor of Six Sigma with the waste reduction and process optimization principles of Lean Manufacturing.

A: The DMAIC methodology stands for Define, Measure, Analyze, Improve, and Control. It is a structured problem-solving approach used in Lean Six Sigma projects to identify and eliminate root causes of process problems, leading to improvement and control of processes.

A: Common Lean tools and techniques include value stream mapping, 5S methodology, just-in-time (JIT) production, Kaizen events, and mistake-proofing (Poka-yoke).

A: Common Six Sigma tools and techniques include statistical process control (SPC), control charts, hypothesis testing, regression analysis, design of experiments (DOE), and root cause analysis.

A: Lean Six Sigma benefits organizations by improving process efficiency, reducing defects and waste, enhancing product/service quality, increasing customer satisfaction, and driving financial savings.

A: Some common challenges in implementing Lean Six Sigma include resistance to change, lack of leadership support, difficulty in sustaining improvements, and the need for cultural transformation.

A: To sustain the benefits of Lean Six Sigma, organizations should foster a culture of continuous improvement, invest in employee training and engagement, establish performance monitoring systems, and ensure leadership commitment and support.

A: Absolutely! Lean Six Sigma principles and methodologies are applicable to various industries, including healthcare, finance, service, and government sectors. The focus is on process improvement and waste reduction, regardless of the industry.


Picture of Daniel Croft

Daniel Croft

Daniel Croft is a seasoned continuous improvement manager with a Black Belt in Lean Six Sigma. With over 10 years of real-world application experience across diverse sectors, Daniel has a passion for optimizing processes and fostering a culture of efficiency. He's not just a practitioner but also an avid learner, constantly seeking to expand his knowledge. Outside of his professional life, Daniel has a keen Investing, statistics and knowledge-sharing, which led him to create the website learnleansigma.com, a platform dedicated to Lean Six Sigma and process improvement insights.

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