What is Miller's Magic Number 7?
In 1956, Harvard psychologist George A. Miller published one of the most cited papers in psychology history: "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information." It established that humans can hold approximately 7 items (±2) in immediate verbal memory.
Miller's contribution wasn't just the number — it was the observation that the limit applies to chunks, not individual bits of information. This is why you can remember "FBI CIA NSA" more easily than "FBICIANSAL" — three chunks vs. nine letters. Chunking effectively bypasses the 7-item ceiling.
The practical impact: Phone numbers are 7 digits long because AT&T and Bell Labs consulted psychologists about the human memory limit when designing the numbering system in the 1950s. This is Miller's number directly encoded into infrastructure.
More recent research by Nelson Cowan (2001) argues the true limit is closer to 4 chunks, with the apparent 7-item limit arising because people automatically group digits during encoding. The Number Memory test lets you see exactly where you fall relative to Miller's range — and how far chunking strategies can take you beyond it.
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George Miller's 1956 paper showed humans can hold roughly 7 (± 2) items in working memory. It remains one of the most cited papers in psychology and explains why phone numbers are 7 digits long.
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