Numbers stay
about twenty seconds.

Your run

Finish a run and this fills in with what your own rounds say — nothing here is written before you play.

Where the number comes from

A digit span is the longest string of digits you can repeat back immediately after hearing or seeing it. The task is about as old as psychology — it was in Binet’s tests before 1910 — and it survives because it takes ninety seconds, needs no equipment, and almost everyone lands somewhere between five and nine.

What it measures is a short-lived holding area. Without rehearsal, items in it fade in something like fifteen to thirty seconds; the classic demonstration is Peterson and Peterson’s in 1959, where filling those seconds with counting backwards wiped most of the list out. The reason you can hold a phone number from the screen to the keypad is not that the store lasts — it is that you keep re-saying it, which writes it back in before it goes.

Seven plus or minus two is not about digits

That phrase comes from George Miller’s 1956 paper, which opens with him complaining that an integer has been persecuting him. It is the most quoted number in psychology and it is almost always quoted for the wrong claim.

1. It was about chunks, not items. Miller’s point was that the limit sits on meaningful units, and that the units are yours to build. 1 4 9 2 is four items to one person and one item to another. Recoding into bigger chunks is how span gets beaten, and Miller said so explicitly.
2. It was never a hard ceiling. Later work tightened it rather than confirming it. Nelson Cowan’s 2001 review put pure capacity nearer four chunks once rehearsal and grouping are blocked. The extra three or four digits most people manage are not capacity; they are technique.
3. Digit span is the easy case. Digits are ten familiar symbols with short names, which is the friendliest material there is. Span for unrelated words is shorter, and for unfamiliar syllables shorter still. A number from the easiest possible material is a poor description of a limit.

Your language changes the score

This is the finding that should make anyone cautious about comparing spans between people. How many digits you can hold depends heavily on how long the digits take to say — even silently. Rehearsal runs at roughly the speed of speech, so a language with shorter digit names fits more of them into the same loop before the front of the list fades.

1. The effect was found inside one head, not between countries. Ellis and Hennelly, in 1980, tested Welsh–English bilinguals in both of their languages. The same people scored lower in Welsh, whose digit names take longer to pronounce. Nothing about the person changed between the two tests.
2. Short digit names run high. Mandarin digit names are short, monosyllabic and quick, and measured spans in Chinese run well above the English figure — around nine or ten rather than seven. English sits in the middle. The gap tracks pronunciation time, not anything about the speakers.
3. So cross-language span numbers do not compare. A span of seven in English and a span of nine in Mandarin can describe the same capacity. Any ranking that puts them in one line is measuring syllables and calling it memory.

The test on this page shows digits rather than reading them aloud, which moves the effect but does not remove it — most people say written digits to themselves as they read. If you speak more than one language, it is worth running it twice and switching which one you count in. The difference is usually visible without any statistics.

Four things that move your result tonight

1. Grouping. Reading 4 9 2 7 1 6 as two three-digit numbers is the single biggest win available, and it is why phone numbers are printed in blocks. It is a real skill, not cheating — but it means the score is partly about strategy.
2. Saying them out loud. Speaking the digits as they appear reliably helps, because it commits them to the loop instead of leaving them as fading images.
3. Interruption. Any thought between the last digit and your first keystroke costs you the front of the list. This is the same mechanism as the 1959 counting-backwards result, at a smaller scale.
4. Tiredness and noise. Span drops when you are tired or being talked at, and the drop is large enough to swamp any difference between two people on a good day.

So the honest reading of a span is narrow: on this screen, in this language, right now, this many. It is not an intelligence score, it is not a clinical result, and a single run of it is not stable enough to compare against a friend’s single run. What it is good for is watching your own number move when you change one thing — grouping, language, time of day — which is the one comparison where everything else is held still.