Miller's Law (7 plus or minus 2)
The observation by psychologist George Miller that the average person can hold approximately 7 (plus or minus 2) items in working memory at once, influencing how information should be chunked and presented.
What Is Miller's Law?
In 1956, cognitive psychologist George Miller published "The Magical Number Seven, Plus or Minus Two," arguing that human working memory can process roughly 5 to 9 chunks of information simultaneously. Modern research has refined this downward (closer to 4 plus or minus 1 for unrelated items), but the principle stands: working memory is brutally limited, and interfaces that exceed this capacity force users to scan, re-read, or abandon. Miller's larger contribution was chunking — grouping items into meaningful units to extend effective memory capacity.
Also Known As
- UX and design: "cognitive capacity limit," "working memory constraint"
- Product and engineering: "chunking," "information grouping"
- Marketing and growth: "rule of 7" (loose, often misapplied)
- Content teams: "scannable lists," "digestible sections"
How It Works
A B2B homepage lists 14 product features in a single uncategorized grid. Users scan, lose track, and forget earlier items as they read later ones. The redesign groups the same 14 features into four themed clusters (Collaboration, Automation, Reporting, Integrations), each with 3-4 features and a category header. Time-to-comprehend the product drops, and engagement with feature detail pages climbs because users can now hold the product shape in working memory while deciding where to click.
Best Practices
- Group navigation and feature lists into 3-5 categories of 3-5 items each; a two-level hierarchy respects the limit at both levels.
- When comparison is required (pricing tables, feature matrices), cap simultaneous options at 3-4 columns.
- Chunk long numbers, codes, and IDs visually (phone numbers, order confirmations, API keys).
- Use category labels that are meaningful, not clever — working memory aids depend on semantic clarity.
Common Mistakes
- Treating Miller's Law as a hard rule ("always exactly 7") when it applies specifically to items held in simultaneous working memory, not browsable lists.
- Reducing count without chunking — five randomly-ordered items can still overwhelm if they lack structural grouping.
Industry Context
SaaS and B2B: feature pages and pricing comparisons are the highest-leverage places to apply chunking; this is where prospects actively hold options in memory. Ecommerce and DTC: product filter groups and variant selections benefit from chunking (Size, Color, Fit rather than one long attribute list). Lead generation: multi-step forms with 3-5 fields per step outperform single-page forms with 15+ fields.
The Behavioral Science Connection
Miller's Law connects to cognitive load theory: when intrinsic load exceeds working memory, extraneous processing kicks in and users lose the thread. Chunking converts intrinsic load into organized structure the brain can cache as a single unit.
Key Takeaway
When users must compare, evaluate, or remember options simultaneously, chunk information into 3-5 groups of 3-5 items — the brain cannot hold more.