Competencies in Six Sigma: Defining Green Belt, Black Belt, and Lean

Management systems are predicated on the performance of personnel, so identifying key competencies for the workers involved is essential for establishing such a system. For example, Six Sigma, a quality management process that is focused primarily on limiting defects, generally recommends the competencies labeled as Green Belt and Black Belt for carrying out the methodology at different levels of an organization.

However, due to the variety of names used for the different competent persons in the Six Sigma process, in addition the different related quality management systems (“Lean” or “Lean and Six Sigma”), there has been ambiguity in their usage among different organizations that advertise sufficient certification in the methodology. This has led to unreliability in the process, as some places claim to possess competency in Six Sigma under conditions that would not be acceptable elsewhere.
ISO 18404:2015 – Quantitative methods in process improvement – Six Sigma – Competencies for key personnel and their organizations in relation to Six Sigma and Lean implementation is the first universal document that compiles and defines the key competencies for individuals in the Six Sigma DMAIC (define, measure, analyze, improve, and control) process.

Yellow Belt

Yellow belts are traditionally those who have a relatively small role in the Six Sigma quality management process, and are only referenced in ISO 18404:2015 as “process operators”. According to the American Society for Quality (ASQ), yellow belts “can be entry level employees that seek to improve their world or executive champions who require an overview of Six Sigma.”

Green Belt

A Green Belt helps to deliver the benefits that have been agreed upon of a quality management system for an organization through improvement activities that are often within the Green Belt’s field of employment and operation. As stated in the standard, this requires Green Belts “to work with the local ‘line management’ to identify and quantify opportunities for improvement within the local environment.”

Because of their concentrated area of operations, Green Belts often work under the direction of a Black Belt or Master Black Belt to carry out Six Sigma processes. They may also coach Yellow Belts in improvement activities and methods.

Black Belt

Similarly, a Black Belt also delivers the agreed benefits of a Six Sigma process, but on a much larger scale. ISO 18404:2015 defines a Black Belt as someone who will work with others to identify and quantify opportunities for improvement, organize multi-disciplinary teams, lead improvement projects, coach and train Green Belts on the DMAIC methodology, and participate in the presentations on the work accomplished through use of the process.

Master Black Belt

The Master Black Belt is the leader of the Six Sigma quality management process, who is expected to support the Black Belts in their execution of the project’s goals. Specifically, a Master Black Belt assists in identifying suitable projects and the determination of their scope, leads the improvement projects, determines the applicability of any training exercises for the organization, conducts periodic reviews of the projects, provides consultancy in advanced statistics, and provides support to fully realize the organizations primary quality management goals.

As Black Belts are often expected to coach Green Belts in the DMAIC methodology, Master Black Belts must do the same for the Black Belts. This establishes the hierarchy of Master Black Belt-Black Belt-Green Belt-Yellow Belt, which secures the effectiveness of selected Six Sigma goals.
Specific competencies needed for the individuals selected to fulfill duties as Green Belts, Black Belts, and Master Black Belts are all addressed in the ISO 18404:2015 – Quantitative methods in process improvement – Six Sigma – Competencies for key personnel and their organizations in relation to Six Sigma and Lean implementation standard.


Some organizations also make use of Lean, a quality management system that can be used in complement to Six Sigma. However, like the different competencies in Six Sigma, Lean has been subject to ambiguity and misuse, even being used interchangeably with Six Sigma.

According to ISO 18404:2015, Lean focuses on reducing chronic waste, while Six Sigma focuses on reducing variation and related adverse effects. Even though it is a different process, Lean makes use of very similar competency levels. These are Lean practitioner, Lean leader, and Lean expert, which can be closely compared to Green Belt, Black Belt, and Master Black Belt, respectively, in Six Sigma.

The key competencies covered in the ISO 18404:2015 document differ among the implemented system in an organization, even though the duties between the different competent persons may greatly overlap. Specifically, the standard addresses all of these competencies for Six Sigma, Lean, or “Lean & Six Sigma.” In the joined system, each level should make use of the combined competencies from both Lean and Six Sigma: Green Belt and Lean Practitioner, Black Belt and Lean Leader, and Master Black Belt and Lean expert.

Further Reading

For a background of the DMAIC methodology: Achieving Quality Through Six Sigma

For information on benchmarking: Six Sigma Benchmarking Criteria for Organizations

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