ISO 9001 vs Six Sigma: Which One Does Your Business Need?

In short: ISO 9001 vs Six Sigma compares two different kinds of thing. ISO 9001 is a quality management standard your whole business gets certified to. Six Sigma is a data-driven method for improving specific processes, and a personal qualification, not a company certificate. Many businesses use both. If your customers want a certificate, that is ISO 9001, and it opens the contracts that ask for it. Get our ISO 9001 templates to build your system without consultancy fees.

People line these two up as if you have to pick a side, and you don't. They do completely different jobs. When I was running businesses I cared about one simple thing: does this help me deliver good work and win more of it? If it's a certificate your customers want, that's ISO 9001, not Six Sigma. Let me explain the difference in plain terms, one business owner to another, so you spend your time and money on the one your situation actually calls for.

Here is the plain difference, with the key points up front in a table.

ISO 9001 vs Six Sigma at a glance

	ISO 9001	Six Sigma
What it is	A quality management system standard: an agreed way of running a business well.	A data-driven methodology for reducing errors and variation in specific processes. The name comes from a statistical target of 3.4 defects per million opportunities, a term first coined by Motorola in the 1980s (Lean Enterprise Institute).
Is it a company certification?	Yes. Your business is assessed and certified against it.	No. It is a method, plus a personal qualification earned in belts (yellow, green, black).
What it is for	Running the whole business consistently and proving it to customers.	Improving a particular process by measuring and cutting out defects.
Who needs it	Any business that wants to run to a recognised standard or hold a certificate.	Businesses and individuals wanting to improve specific processes, often in manufacturing or operations.
Do they work together?	Yes. ISO 9001 sets the framework.	Yes. Six Sigma can be one of the tools you use to improve within that framework.

The simplest way to think about it

ISO 9001 is the framework for running the whole business well and proving it. Six Sigma is a toolkit for making a specific process better. One is about the system as a whole; the other is about sharpening a particular part of it.

That is why the "which is better" question does not really work. It is like asking whether a set of house rules is better than a particular power tool. They do different jobs. A business can hold ISO 9001 certification and use Six Sigma methods inside it to drive improvement. Neither cancels the other out. The same goes for a SWOT analysis, a popular way to work out your strengths, weaknesses, opportunities and threats. ISO 9001 requires you to identify the internal and external issues and the risks that affect your business, and a SWOT is one handy tool for doing it.

The other names you will hear: Lean and TQM

Two more terms come up in the same breath, so briefly and neutrally: Lean is a method focused on removing waste and speeding up flow, and TQM, total quality management, is a broad philosophy of continuous, company-wide improvement. Like Six Sigma, these are approaches and mindsets, not standards you get a business certified to. ISO 9001 is the one that gives you a certificate. The others are ways of working you can adopt alongside it, and all of them are perfectly respectable in their own right.

So which one do you actually need?

It depends on your goal. If a customer or contract is asking you to be certified, you need ISO 9001, because that is the one you can hold a certificate for. If your aim is to fix a specific process that keeps producing errors, Six Sigma methods may help. Many businesses do both: get certified to ISO 9001 for the framework and the credibility, and use improvement methods like Six Sigma or Lean within it. If you are starting out and someone has asked for a certificate, start with ISO 9001.

New to all this? Our plain-English guide, what ISO 9001 is, explains the certificate side from scratch, then the free readiness quiz shows where you stand.

Frequently asked questions

What is the difference between ISO 9001 and Six Sigma?

The difference is that ISO 9001 is a quality management standard your whole business gets certified to, while Six Sigma is a data-driven method for improving specific processes and a personal qualification earned in belts. ISO 9001 proves the business runs to a recognised standard; Six Sigma is a toolkit for reducing errors in a particular process. They are different kinds of thing and often used together.

Which is better, Six Sigma or ISO 9001?

Neither is better; they do different jobs, so the right one depends on your goal. ISO 9001 is what you need if you want a certificate proving your business meets a recognised standard, while Six Sigma is a method for improving a specific process. Many businesses use both, so it is rarely a case of choosing one over the other.

Can you use ISO 9001 and Six Sigma together?

Yes, ISO 9001 and Six Sigma work well together, because they operate at different levels. ISO 9001 provides the overall framework for running and proving your quality system, and Six Sigma is one of the improvement tools you can use within that framework. Using both gives you the recognised certification and a structured way to keep improving.

Is Six Sigma a certification like ISO 9001?

Not in the same way; Six Sigma certification is a personal qualification for individuals, earned in belts, whereas ISO 9001 certifies an entire business. When someone is "Six Sigma certified" it means they have trained in the method, not that their company has been assessed. ISO 9001 is the one that certifies the organisation itself.

Is ISO 9001 the same as ISO 9000 or Six Sigma?

No, all three are different: ISO 9000 explains the principles and vocabulary of quality management, ISO 9001 is the standard you get certified to, and Six Sigma is a separate process-improvement method. Only ISO 9001 gives your business a certificate. The others are background knowledge and improvement tools respectively.

If the certificate is your goal, ISO 9001 is the one that counts. See how ready you are with the free readiness quiz, no email required.

About the author

Written by Mike Armstrong, senior ISO consultant, former company director, and founder of Plain Standards. In over 30 years running companies at director level, Mike built his own management systems to drive profit long before he adopted ISO 9001, so he comes at this from the owner's side, not the auditor's. Plain Standards helps small and medium sized businesses get ISO certified without a consultant.