Textbook of Usability

Also known as: The Magical Number Seven, Miller's Magic Number

Miller's Law comes from George A. Miller's 1956 paper "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information". Miller observed that human short-term memory could hold about 7 ± 2 chunks of information.

A "chunk" is a meaningful unit. The string "XCNLBC" is six chunks (each letter), but if you reorder it as "CNN BBC LX" you've created three chunks (familiar acronyms), which is much easier to remember.

Modern research has revised the number downward — working memory is now thought to hold only about 4 ± 1 chunks of new information. Miller's original 7 ± 2 was based on tasks involving familiar items where chunking was easier.

Design implications:

• Chunk information into meaningful groups (phone numbers as 3-3-4 digits)
• Don't expect users to remember more than a few items at once
• Reduce options in any single decision point
• Use external memory (notes, lists, persistent UI) to offload cognitive work

The law is widely (and often incorrectly) cited as justification for limiting menus to 7 items. Miller himself never made this claim. The actual implication is that novel information should be limited and chunked.