Miller’s Law Explained

miller's law

Introduction: What is Miller’s Law?

Ever wondered why the standard American telephone number has seven digits? I guess we all have heard of the magical number 7, but why is it called magical and is it indeed? Let us find out. In 1956, George A. Miller discussed this question in his article titled “The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information,” which was published in The Psychological Review, and known as Miller’s Law.

In the article, Miller said he was persecuted by an integer: 7. He stated that the number of objects an average person can hold in his or her working memory is about seven (plus-minus two).

Now, what is this working memory that Miller is talking about in his law?

Working memory is our ability to remember and use relevant information while in the middle of an activity, for example, while playing a game when you recall the rules of the game or when you are recalling the steps of your favourite recipe while cooking it then you are using your working memory.

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Miller proposed that our working memory has a certain capacity to hold information. His magic number 7 (plus-minus 2) provides evidence that most adults can store between five and nine items in their short-term memory. He thought that working memory could hold 7 (plus-minus two) items because it has a limited number of “slots” in which information could be stored.

Miller also explained that there is a possibility that this limit could be extended. Since he did not specify how much information can be stored in these slots, the limit could be extended by the process of “chunking” that is to bundle the information into small “chunks” and then storing it. The plus-minus two that is there in his number was his way to give space to variations which could come due to chunking.

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Modern-day psychologists believe that we have already passed our upper limit of storing information into our working memory with the introduction of 10-digit phone dialling. For example, to memorize a ten-digit phone number, we all break down the number into smaller chunks like 98-670-984-01 and then store into our memory.

Research Supporting Miller’s Law

Miller’s theory is supported by psychological research. Jacobs conducted an experiment in 1887 using a digit span test, to examine the capacity of short-term memory for numbers and letters. Jacobs used a sample of 443 female students between the ages 8-19 from the North London Collegiate School.

Pacific Northwest National Laboratories researchers at the Bioproducts Sciences and Engineering Laboratory at WSU-Tri-Cities use a robot to prepare high throughput samples for a variety of projects.
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Participants had to repeat back a string of numbers or letters in the same order and the number of digits and letters were gradually increased until the participants could no longer recall the sequence. Jacobs found that the student had an average span of 7.3 letters and 9.3 words, which supports Miller’s notion of 7+/-2. Can you recall a game based on this experiment? Remember the game memory? I guess now we know the inspiration behind that game.

Although Miller’s theory is supported by psychological research, he did not specify how large each ‘chunk’ of information could be. Consequently, further research is required to determine the size of information each ‘chunk’ can hold to understand the exact capacity of our working memory.

Application of Miller’s Law

One of the key concepts behind Miller’s Law is ‘chunking’, which means assembling various bits of information into a cohesive gestalt. Chunking is a critical element of information organization and is the basis of today’s user experience design. User experience design is about enhancing the experience that people have while interacting with your product.

One of the display units at the Discovery Center of the Centennial Hall.
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There is an organizational rule based on his theory which states that ‘Always organize elements of information in categories no larger than 9, but preferably five chunks.’ The more chunks of information you add to an ‘interface’, the more difficult it becomes to ‘work’, using the information at hand.

Due to the limitations of working memory, as a product becomes more feature-full it inevitably becomes more difficult to use, because the user has to manage more information while operating your product. Today’s technology is all about optimizing information in a user-friendly way. Miller’s Law helps us understand the need for creating such optimizing search results for our users.

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One good example is Netflix. It reduces the number of shows shown to its users to prevent cognitive overload by grouping them into different categories. They even go a step further by only showing the categories that the users are interested in based on their previous viewing history.

Miller’s Law applies to our everyday life as well. Be it remembering a list of groceries to buy or quickly mugging up the phone number of a relative your mother is dictating and you have nothing to note it down, Miller’s Law explains how we process such information. It also teaches us that humans can process only a finite amount of information, and that information overload will lead to distraction that negatively affects performance.


It’s fair to say that Miller’s Law is very much relevant to the modern-day society and relates to our everyday lives as well. a law founded in the ’90s is still relevant and used in today’s technology.