Number Memory Test

Digit span, and the most quoted number in psychology

What this test measures has a name: digit span, the count of digits you can repeat back immediately after seeing them. It is one of the oldest measures in the field, it sits inside most standard intelligence batteries, and it is the source of a figure almost everybody has heard. Seven, plus or minus two.

That figure comes from a 1956 paper by George Miller on the limits of immediate memory, and it has been repeated so often that it has hardened into folklore. The paper itself was more careful than its reputation. Miller's point was not that the mind holds seven things. It was that the capacity is fixed in chunks rather than in raw items, and that what counts as a chunk is entirely up to you. Later work put the real limit on unrelated items lower, nearer four. The gap between four and seven is chunking, and you can watch yourself doing it on this page.

How to read your score

Watch yourself chunk

Up to about six digits you probably hold the number as a plain string of sounds, rehearsing it in your head. Somewhere around seven that stops working, and something else takes over without being asked to.

You start finding the number inside the number. A 1987 in the middle stops being four digits and becomes a year. A 404 becomes an error. A 3141 becomes pi. Your own phone number, a house number, a shirt size. Each of those is one chunk occupying one slot, and a slot can hold four digits as easily as one. That is why a person with an average span of seven single digits can sometimes carry fourteen digits that happen to fall into familiar groups.

It is also why this test rewards practice so steeply, and why a very high score says more about technique than about capacity. The people who reach twenty digits are usually using a deliberate system, most often converting digits into consonants and consonants into words, and then remembering a short absurd sentence instead of a long number.

Why the number is spoken in your head, not seen

Digits are unusual among the tests on this site because they are verbal. You do not really remember what the number looked like, you remember what it sounded like, held in a rehearsal loop that refreshes itself every couple of seconds. Which has a practical consequence: talking, or listening to anything with words in it, competes directly for that loop and will cost you digits. Instrumental music interferes much less.

Compare that with visual memory, which uses a spatial store instead and is barely affected by speech, or sequence memory, where most people improve dramatically as soon as they invent names for the tiles and drag the task into the verbal system on purpose.

Getting a fair reading

Do it once, cold, before you read the advice above, if you want your actual span. After that you are measuring how well you have learned the game, which is a perfectly interesting thing to measure but is not the same number. Run it in a quiet room, do not say the digits out loud, and do not retry six times and keep the best. Your best of six is not your span.

The chimp test is the hardest of the memory group here because it demands position and order together. If you would rather test speed, the reaction time test is the flagship.