Miller's Law
Working memory holds a small number of chunks, so the design lever is what counts as a chunk, not the raw item count.
Definition
George Miller's 1956 paper reported that the span of immediate memory is limited to roughly seven chunks, plus or minus two, and that people expand effective capacity by grouping information into larger meaningful chunks rather than by holding more items.
Established research. Originates in published research and has been replicated. The effect is real. Its size in your product still needs measuring.
On this page
What is genuinely useful here
The durable insight is chunking. A ten-digit phone number is at the limit of memory as ten items and comfortably inside it as three chunks. The same restructuring works on interfaces: an eighteen-field form is unmanageable as a flat list and reasonable as five labelled groups.
The second insight is that working memory only binds on information the user must carry across a boundary. Anything visible on screen is not in working memory, it is in the environment. Interfaces reduce memory load mostly by keeping things visible, not by shortening lists.
Design moves that follow from chunking
- Format long numbers into groups: card numbers in fours, phone numbers by country convention, IBANs in fours.
- Group form fields into labelled fieldsets that map to real-world concepts, such as delivery address and payment.
- Keep the summary of a multi-step flow visible so the user never has to remember what they entered two steps ago.
- Show the query in a search results header, since the user should not have to recall what they typed.
- Split dense tables into logical column groups with a header spanning each group.
Applying it honestly
Do
- Reduce what has to be remembered across screens.
- Chunk by meaning, so the group has a name a user would recognise.
- Persist entered data when the user navigates back.
Do not
- Cap navigation or list length at seven for its own sake.
- Cite the paper as evidence for a specific item count.
- Assume chunking helps when the groups are arbitrary. An unlabelled group of four is not a chunk.
In practice
Card number entry
CheckoutAuto-formatting a card number into groups of four as the user types lets them verify against the physical card in four glances instead of sixteen, and reduces transposition errors.
Grouped settings
Application settingsSixty settings under six named groups is navigable. The same sixty in one alphabetical list is not, even though the item count is identical.
Sources
Where a source establishes something narrower than the popular reading of it, the note says so.
The magical number seven, plus or minus two
G. A. Miller, Psychological Review, 1956
The magical number 4 in short-term memory
N. Cowan, Behavioral and Brain Sciences, 2001
Reassessment placing the capacity limit closer to four chunks.
Continue from here
Each link says what the connection is, so you can tell a principle from an alternative from a thing people mix this up with.
Applies when you are designing
Applied through
Where this shows up as a concrete interface decision.
- Information ArchitectureResearch method
- ProximityUI foundation
- Visual HierarchyUI foundation
Commonly confused with
Close enough to be mixed up, different enough to matter.
- Hick's LawLaw
Hick's is about decision time under choice. Miller's is about holding items in memory, and is routinely misquoted as a limit on menu length.
Short definition
The one-paragraph version, for when that is all you need.
- ChunkingTerm
- Cognitive LoadTerm
Related concept
Connected closely enough to change how you apply this.
- Recognition Over RecallHeuristic
- Serial Position EffectLaw
- Progressive DisclosurePrinciple