How is Lean Different from Six Sigma? Lean is elimination of waste. Six-Sigma is about elimination of variation. Pick the right tool for the right purpose.

The Difference Between Lean and Six Sigma

Six-Sigma’s goal is to produce output that is consistent and free of defectsDefective output requires re-work and re-work is waste.  Inconsistent output is the result of a flawed processSix-Sigma seeks to identify the flaws, determine their cause, and eliminate them. 

Six Sigma DMAIC starts with the view that waste is defective products, to remove waste you find the root cause of defects (using statistical methods) then design an improvement (Design for Six Sigma) or replace a fault so that the defects no longer occur.

Using a manufacturing example again, let’s say you have a factory that produces widgets.  The widgets are all supposed to be a certain size, shape, and weight.  You sample your output and discover that out of every 1,000 widgets fifty are flawed (e.g. wrong size, shape, or weight).  To correct this you could use Six-Sigma to determine what’s causing the variation/defects and work to reduce them to a six-sigma level.

Lean must begin with the view that the product and process that creates it must add value to the customer. Anything that does not directly add value to the customer is a waste. It further goes on to define the common wastes and how to eliminate them.

Lean vs Six Sigma

While it may be desirable to use both lean and Six-Sigma, they are separate issues.  An operation can be lean and still have an unacceptable level of variation in the output.  It can also have the variation under control and not be lean.  The two are complimentary, but neither is dependent on the other.

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While Lean encourages daily, general improvements, Six Sigma demands data-based, specific improvements for specific projects.

Lean doesn’t require a hierarchical structure of qualified “masters” to implement the changes. Every individual employee, regardless of their roles in the business is encouraged to participate in actively improving the manufacturing process.

Six sigma requires a hierarchical structure of various experts with various belts, signifying their level of experience and knowledge in the Six Sigma way.

With the Lean approach, you can walk into your factory today and instruct everyone on what to look for and give them methods for applying changes they see fit.

With Six Sigma, you’ll have to hire a certified expert who will assemble a team, identify a problem, and direct that team until the problem is solved.

In Lean, you let everyone test and experiment to see what works and what doesn’t – a bottom-up approach.

In Six Sigma, you let the qualified professional leading the team decide when you’ve completed the project – a top-down approach.

Which to do first? Lean or Six Sigma?

Undoubtedly in an ideal world you should do Six Sigma before lean.

Why should you do six sigma before lean? Because lean is about creating an efficient process and six sigma is about making the process deliver what the customer wants with little variation. You don’t want to do lean first because you could make a perfectly-efficient, process that delivers something that the customer doesn’t want.  If something doesn’t need to be done in the first place, there is no point in doing it well.

If you do Six Sigma first, you’ll have a process that can reliably produce output that the client wants repeatedly. Then, use Lean to make that process very efficient and productive.

In other words, use Six Sigma when your process has a lot of variation or doesn’t always perform how the client wants it to. Use Lean when your process already delivers what the customer wants but the process itself needs to be more efficient or more productive.

Both are tools, philosophies and management systems but geared towards different ends.

It is very possible that both processes could use the same or similar tools and end up with the same improvements.

Note that in the real world some management teams are more focused on efficiency and productivity than customer satisfaction, and in those cases Lean is the best choice. Also, it is sometimes helpful to do quick Lean activities so you can show improvements quickly (whether or not the customer cares about them) so you can build credibility to do the longer Six Sigma projects.

Tools Used by Both Six Sigma and Lean

In both cases process mapping and value stream mapping are essential. If you cannot define your process, how can you possibly know what is wasteful or what is variation? Once you have defined your process via a process map you can use value stream analysis to determine where the waste is.


Comments (12)

Author does not understand lean. Beginning with 6sigma regularly creates an enormous amout of waste, frustrates employees….especially those who know the customer best.

If this was part of 6Sigma for Dummies it explains a lot. Thoroughly understand lean….read ‘The Goal’ and Six Sigma before moving forward with your six sigma squads. Terrible, terrible advice you’re giving.

When I read the article above, I also disagreed with the comment do 6sigma before lean. This was because I recalled a situation where we flow-charted a process, and ended up removing a whole sub-process that was being delivered due to historical inertia. – we have always done that because that is what they need!

Had we spent time controlling the sub-process first, that would have been wasted effort. I would have thought that the first step should always be to determine what the customer supplier chain should be delivering, and then ensure that it is being controlled.

This was under TQM though, and i have just started to look at Lean and 6sigma, so i may be missing the actual application here.

Great site though.

Hi Ian, Good points. I think you and I are coming from a similar perspective.

Let’s assume the process is delivering something that is wanted by the customer. And beyond that, there are quality standards meaning that something could be wanted and created badly.

If you have poor quality (or a lot of variation in quality), my logic is that you want to get that under control first. If you speed up the cycle time using lean, you just get even more defects – just quicker.

Writing this reply, I could envision scenarios where you might do lean first or even in conjunction with Six Sigma – so my article above may come across more absolute than I had meant it to be.

I think it all comes down to a cost of poor quality analysis at the start of the project. If your process has stability and great quality, then go ahead and lean it out – the ROI will likely justify it. However, if you have poor quality, the ROI of Lean is likely less than stabilizing the process and improving the quality.

And again, I mention ideal scenario. Any practitioner of any quality system (Lean, Six Sigma, TQM, etc) has been exposed to the reality of needing to achieve a “win” quickly in order to keep the program going.

I agree with Ted. A business’ sole purpose is to create value for an end user. The Six Sigma approach emphasizes the need to create and build value for the customer, thus maintaining and growing the business.

Lean is still very important, but if you implement Lean without fully recognizing what is creating value for the customer, the profits gained from Lean will only last as long as value is provided to the customer.

Well, in my opinion,
writer’s has good enough view for both from his own deep enough knowledge.
Only thing is in short. agree.

Sometimes people have different understanding about lean as lean is actually an explanation of Toyota Production System, so discussion related to lean might not be easy.

I think lean (or Toyota Production System) can be worked alone very well without six sigma, actually both methodology emphasis customer value, so there is no answer for which one should go first, it actually depends on what kind of problem that your company is facing.

Hi! A few questions:
– Is it necessary to implement the six sigma methodology if a company is already fully-optimized as a lean organization?
– Is it necessary to implement the lean methodology if a company is already fully-optimized as a six sigma organization?


Hi Jack,

I don’t see lean and six sigma as mutally exclusive. In other words, you want to choose the right tool for the job.

First question: “s it necessary to implement the six sigma methodology if a company is already fully-optimized as a lean organization?”
Well, nothing is necessary. But if you want to compete, I would think you should. Six Sigma is about executing flawlessly (or as close to it as possible). Lean is about removing waste. If you focus on lean first you run the risk of optimizing processes that shouldn’t even exist in the first place – or that should exist in a fundamentally different way.

Second question:
“Is it necessary to implement the lean methodology if a company is already fully-optimized as a six sigma organization?”
This comes back to your KPIs, countermetrics, and goals of your organization. Let’s say you used Six Sigma to reduce error rates in a process. You were also responsible so you made sure the project aligned with company goals on the outset. Also, you established countermetrics to ensure that your changes never made a negative impact to another part of the company. But now that you have a very accurate process you’d like to scale and increase output. One way to do that would be to lean out the process to remove as much waste as possible and increase resource utilization WHILE maintaining the gains Six Sigma gave you.

this makes a lot of sense. I just hope it worded where I can understand what’s being asked during the exam.

Yellow is for existing processes 1,2,3 lead with lean
Blue is new processes 3,2,1 lead with VOC

Moving on…

I got confused between these 2 lines
1=”Lean must begin with the view that the product and process that creates it must add value to the customer”

2=”some management teams are more focused on efficiency and productivity than customer satisfaction, and in those cases Lean is the best choice”

Hi Nabeel,

Thanks for asking. The distinction is really a case of Ideal vs Reality.

In the Ideal state, you would evaluate a tool before using it. Lean requires a focus on the value to the customer and the discipline to trace that value backwards through all process that deliver that value and increasing it. In that case, you would choose lean to eliminate all items that get in the way of value delivery.

However, some management teams pre-select the symptoms they want to address rather than focusing on true end-to-end value. In those cases you’ll hear phrases like “we need to reduce cost” or “we need to improve cycle time” – but without any answers to the why that kind of project is selected ahead / instead of something else. In those cases, use Lean.

All of this is in opposed as to the question of ‘When do you use Six Sigma?” My practical answer to that is “Use Six Sigma when you have a defined process that delivers value to the client which you wish to maximize AND you have no good idea how to accomplish that.”

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