If you’ve heard of Lean, you’ve likely heard of Six Sigma. Because much of modern-day Six Sigma is rooted in Lean manufacturing practices, it’s easy to confuse the two – which is why many mistakenly use the terms interchangeably.

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Both Lean and Six Sigma are business methodologies that aim to improve efficiency and effectiveness in organizations risks.
Both Lean and Six Sigma are business methodologies that aim to improve efficiency and effectiveness in organizations risks.

While both Lean and Six Sigma are business methodologies that aim to improve efficiency and effectiveness in organizations, there are theoretical and practical distinctions between them. Understanding these differences can help you choose a methodology that aligns with your business’ goals. Learn the subtle distinctions between Lean and Six Sigma to help determine which might be right for your organization.

Lean vs. Six Sigma: Similarities and Differences

Defining waste

From a theoretical perspective, one major distinction between Lean and Six Sigma is how practitioners of these methods identify waste: In Lean, waste is defined as any process or activity that does not add value to the customer. In Six Sigma, waste results from variation within a process.

This means that Lean practitioners focus on optimizing processes to create value, while Six Sigma proponents aim to eliminate defects and waste by reducing variability.

History and goals

Modern-day Lean and Six Sigma practices both were born in complex manufacturing environments – specifically, automotive manufacturing in Japan. As Western manufacturers began adopting the practices and principles used by Japanese manufacturers, different versions of Lean were developed.

Lean and Six Sigma share the same ultimate goal: Both seek to eliminate waste and increase the efficiency of a system as much as possible.

However, since the definition of the root cause of waste differs between these two methods, the approach to achieve that goal differs as well.

Mindset vs. practice

One fundamental difference between Lean and Six Sigma is that Lean is a mindset – a set of principles that, when applied holistically, enables smarter decision making. Lean thinkers apply the continuous improvement method to continuously identify ways to increase value and eliminate waste. Anyone can be a Lean thinker; in fact, Lean is most effective when it is embedded into the culture of an organization and applied from the ground up.

Six Sigma is a program: A methodical, structured approach to tackling organizational problems by eliminating variability and reducing risk. One of the most recognizable elements of Six Sigma is its certification system. Six Sigma professionals exist at every level in the organization, each with distinct roles and responsibilities. Here is a basic rundown of Six Sigma certifications (taken from ASQ):

  • Black Belt: Leads problem-solving projects. Trains and coaches project teams.
  • Green Belt: Assists with data collection and analysis for Black Belt projects. Leads Green Belt projects or teams.
  • Master Black Belt: Trains and coaches Black Belts and Green Belts. Functions more at the Six Sigma program level by developing key metrics and the strategic direction. Acts as an organization’s Six Sigma technologist and internal consultant.
  • Yellow Belt: Participates as a project team member. Reviews process improvements that support the project.
  • White Belt: Can work on local problem-solving teams that support overall projects, but may not be part of a Six Sigma project team. Understands basic Six Sigma concepts from an awareness perspective.


With these different certifications, Six Sigma provides a structured, hierarchical model for leadership that is well-suited for highly structured organizations. Certification programs prepare Six Sigma professionals to perform a specific role in their organization, usually starting with localized problem solving, working their way up towards leading complex problems and training project teams.

Lean allows for a bit more fluidity, encouraging all practitioners to think big and solve organizational problems, regardless of whether they’re an individual contributor or an executive. While it can be successful in more structured environments, Lean is well-suited for flatter, more autonomous organizational structures that enable collaboration across departments and management levels.

Functional areas

Modern Lean practices come from software development, where they are still applied today (either as true Lean practices, or Lean offshoots such as Agile, Scrum, or Kanban). Teams and organizations in all functional areas are using Lean principles to create more value for their customers.

Six Sigma remains firmly rooted in complex environments where decreasing variability and reducing risk is critical for success. Six Sigma can be applied in a variety of functional areas, such as engineering, manufacturing, plant operations, as well as sales/marketing and customer service, but it’s not right for every company or process. Many small companies lack the resources required to implement Six Sigma.

Which Is Right for You?

If your organization is looking for a lightweight, continuous methodology to guide innovation and improvement, Lean might be an ideal fit. If you’re looking to reduce variability and risk in a more complex environment, Six Sigma might be better suited for your needs. While some organizations intently choose one over the other, many choose to infuse their Six Sigma implementation with Lean principles, into a hybrid methodology known as Lean Six Sigma.