Simpler Definitions of Muri, Muda and Mura

By Jon Miller Updated on December 6th, 2020

In the Lean lexicon are three Japanese words that describe the nature of losses in a system. They are muri, muda and mura. In English these are often translated as overburden, waste and variation. The seven types of waste are well-known by now. For many organizations, the main focus of the Lean approach to continuous improvement is to identify and remove wastes from all processes.

Reducing variation is long-standing focus of the quality movement. Oddly, there is no equivalent movement or field focused on reducing overburden. The closest we come to this are certain industrial engineering, EH&S, and human factors disciplines. These primarily address physical burdens and unsafe conditions. Overburden is a risk not only a physical and mental risk to people. It also threatens machines, systems, policies, equipment, ecosystems – the list is long.

How Not to Lose Sight of Muri and Mura

Overburden and variation are general conditions. There are no tidy numbered lists to categorize them. They are easy to lose sight of. Overburden and variation are not as visible as waste. They are often viewed as underlying conditions that result in one or more of the wastes on the surface. When we attempt to power through the conditions of overburden or variation rather than correct them, we create excess stock, defects, motion and transportation.

When we focus too much on pointing out and removing the superficial wastes, we may do so at the expense of addressing causes of burden and variation. Perhaps it’s simply a matter of pausing in the face of one of the 7 types of waste to ask ourselves, “How did overburden or variation generate this waste?” Or maybe it would help if we could simply the definition of these three under a common frame of understanding.

A Simpler Definition of Muri

Muri word is typically translated as overburden, overwork or unreasonableness. When we expect unreasonable things from our processes, people, systems, strategies and so forth, this is muri. People, equipment, systems, etc. break when we push too hard. They break, resulting in waste and other poor outcomes. Perhaps a simpler definition of muri would be any condition in which the requirements we place on our processes is in excess of their capability.

A Simpler Definition of Muda

Although it’s a popular definition, it’s not completely accurate to say that muda is any activity that consumes resources while adding no value. With the exception of creating defects, creating waste often comes with value. Inventory, motion, transportation, waiting and overproduction are part and parcel to the value-added transformation. The waste of processing itself, a.k.a. over-processing, is a value-added step. It does the job. It’s just poorly designed. Perhaps a simpler definition of muda would be any condition in which the inputs or outputs of a process are excessive.

A Simpler Definition of Mura

A simpler definition of mura is any condition in which there is a mix muri and muda. Sometimes we demand too much from our processes, and sometimes the inputs and outputs of our processes are excessive. Of course, randomness and natural variation exists within systems. But this is the tricky part. This is not mura. There is a different word for that. Only when humans view variation as outside of tolerance limits, a problem or gap against our expectation for a process does it become mura.

Putting It All Together

Muri, muda and mura are small words that pack in some big ideas. There is an interrelationship. If we hope to make an impact on waste, variation or overburden, we need to consider them as a set. We can describe these concepts together as “Experiencing losses due to a failure to fully understand our processes.”

This of course assumes that humans, after understanding their processes thoroughly, will act rationally. Based on understanding, we will not make unreasonable or burdensome demands on people and processes.  My understanding of humanity suggests that this may be asking too much. We have great variation among us.

What do you think? Does this new set of definitions help in bringing a cohesive explanation of muri, mura and muda? Does it try to do too much? Is it just undesirable variation? Or is it a waste of time?

  1. Fabio

    January 29, 2021 - 12:21 pm

    Thanks Jon, great explanation. I think it was cohesive and clear enough. I see great utility mainly when we will go to set and realize the objectives and expectations when we’ll go aboard kaizen projects. Understand the actual process in a clearly way will give us an idea to set the honest process we deserve and establish the challenges everyone will face as a whole.

  2. Brion Hurley

    January 30, 2021 - 3:42 pm

    Good article. Would it be correct to state Mura as excessive variation (special cause, unexpected), and we should not call it Mura if it is simply common cause variation (typical variation, expected)?

    Also, any tips for remembering the difference between Mura and Muri? The only thing I have come up with is Muri end in “i” and I remember an individual, and that makes me think about them be stressed out and overworked.

  3. Jon Miller

    January 30, 2021 - 8:25 pm

    Hi Brion

    Yes, that’s part of it. It’s also a question of where we set the acceptable standard or specification. When we paint a wall, finish may not be perfectly even if examined under a microscope. There will be mura. But it’s completely acceptable. But we would raise claims if one area was patchy or a noticeably different tone.

    Muri ends in “I”. Remember “I” for “impossible” which is another meaning of the word and similar enough to “unreasonable” or “overly burdensome”.

    Mura ends in “A” which I suppose you could think of as deviating from “average” or “acceptable”.

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