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UX glossary · engl. Miller’s Law

Miller’s Law

Miller’s Law describes the observation that people can only hold a small number of information units in short-term memory at once. Miller suggested about seven in 1956; newer research points to about four.

Imagine someone reads you a customer number over the phone: “4 8 1 9 2 7 3 0 5 6 2.” You don’t have a pen and try to keep it in your head. By halfway through, you’re struggling. If the person says “481, 927, 305, 62” instead, it’s much easier.

That difference is what Miller’s Law is about.

Explained simply

In 1956, psychologist George A. Miller published the paper “The Magical Number Seven, Plus or Minus Two.” In it, he described how people can only keep about seven units in short-term memory (the store for what you’re holding in mind right now), give or take two.

What Miller found most interesting was that these units aren’t single letters or digits, but meaningful groups called chunks. Seven single letters are about as hard to remember as seven short words, even though the words contain many more letters. An everyday comparison: you remember a date like 14 July 1989 as day, month and year, three chunks rather than a long string of digits.

What research says today

The “seven” is more of a rough rule of thumb than a fixed measure, and Miller himself used “magical” rhetorically. In a widely cited 2001 review, Nelson Cowan concluded that pure capacity is closer to three to five chunks, about four on average. How much actually fits also depends on the material, prior knowledge and the situation.

For more on the basics, read Basics of Human Perception: Short-Term Memory.

Common misconceptions

The best-known misconception goes like this: “A menu can have no more than seven items.” Miller’s work doesn’t support that. The limit applies to things you have to remember without seeing them. A menu, however, is visible on screen. People recognize the right option there instead of recalling it from memory. The Nielsen Norman Group explicitly calls the seven-item rule for menus a misconception. A well-structured menu with ten clear entries can work better than seven abstract umbrella terms.

An example

Here’s an example: a payment form asks for an IBAN (the international bank account number used in Europe) in a single field without spaces. Anyone typing it from an invoice keeps losing their place and ends up checking it digit by digit.

After the redesign, the field automatically groups the input into blocks of four, the way it usually appears on invoices and bank statements. The number is the same, but it now breaks down into easy-to-scan chunks.

In practice

  • Break information into chunks. Numbers, long texts and forms get easier when you split them into meaningful groups, for example with subheadings or spacing.
  • Favor recognition over recall. Show important information where people need it instead of making them remember it across several steps. This reduces cognitive load.
  • Don’t use seven as an excuse. Decide how many menu items you need based on content and testing, for example with card sorting, not based on a number. You’ll find more principles in the Laws of UX resource.

Related terms

Working Memory, Cognitive Load, Hick’s Law, Progressive Disclosure

Sources

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