The art of thinking · 3 · Memory

Working memory capacity

Also known as: Memory span, Short-term memory capacity, Magical number seven

German: Arbeitsgedächtniskapazität

In cognitive psychology, working memory capacity is the amount of information a person can hold in an active, accessible state at one time, usually measured in chunks; current estimates put the limit at about three to five chunks for young adults when rehearsal and grouping are prevented, and capacity differs between individuals.

Cognitive psychology
Memory

In one sentence

Working memory capacity is how much a person can hold active at once — about four chunks (Cowan, 2001); “seven plus or minus two” is no design rule.

Example

A style guide limits procedures to “seven plus or minus two steps” and cites Miller (1956). The paper is about the span of immediate memory for items such as digits, not about how many steps a reader can follow on a page in front of them.

What the research shows

George A. Miller (1956) observed that absolute judgments of one-dimensional stimuli and the span of immediate memory both seemed limited to around seven items, and showed that recoding items into larger units (chunks) lets people remember far more material. Nelson Cowan (2001) reviewed later evidence and concluded that Miller's seven was meant as a rough estimate and rhetorical device; when rehearsal and chunking are controlled, the limit is about three to five chunks, often summarized as four. Cowan (2010) restated this for a general audience. Measures such as reading span (Meredyth Daneman and Patricia A. Carpenter, 1980) show that capacity differs between people and predicts performance in comprehension tasks.

Evidence status

A capacity limit is well established; its size depends on what is counted as a chunk, on the material and on whether rehearsal is possible, so it is not a fixed number of words, steps or items. The popular rule “seven plus or minus two” for menu items, bullet points or procedure steps is not derived from Miller's paper: Miller described laboratory span tasks, and a reader of a procedure sees the steps on the page instead of holding them in memory. Step-count limits in style guides are editorial conventions, not findings from capacity research.

How it applies

Capacity limits matter where readers must hold information without seeing it — values to carry from one place to another, conditions to remember, codes to enter. The glossary “Applied cognitive psychology for information use” treats the design side; cognitive load theory builds on the limit. A procedure's length should follow the task and its checks, not a number attributed to Miller.

External references

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