Digit Span Test: How Many Numbers Can You Remember?

A digit span test measures how many digits you can hold in mind at once. Someone reads you a string of digits and you repeat it back, first in the same order (forward span) and then in reverse (backward span). The lists get longer until you miss, and the longest list you get right is your span. In one study, adults aged 18 to 65 averaged about 6.4 digits forward and 4.6 backward, while a smaller group of young adults averaged about 7.4 and 5.8 (Woods et al., 2011). Those numbers line up with George Miller’s famous “seven, plus or minus two” from 1956 (APA PsycNet). Later work by Nelson Cowan puts the deeper limit nearer 4 chunks (Cowan, 2001).

How the test works

Forward and backward digit span are among the oldest and most widely used tests of short-term verbal memory (Woods et al., 2011).

Forward span

You hear a list such as 5-8-2 and say “5, 8, 2.” In the Wechsler Memory Scale (WMS-III) version, forward testing starts at three digits, and you get two lists at each length (Woods et al., 2011). The test stops when you miss both lists at a length or reach the maximum, which is 9 digits forward (same source).

Backward span

You hear 5-8-2 and say “2, 8, 5.” Backward testing starts at two digits and tops out at 8 (Woods et al., 2011). You have to keep the list in mind while you reverse it. In a review for neurologists, Sandra Weintraub groups digit span with tests of attention and calls backward span a test of working memory (Weintraub, 2022).

Sequencing

The fourth edition of the Wechsler Adult Intelligence Scale (WAIS-IV) added a third part, Digit Span Sequencing (Egeland et al.). It asks you to say the digits back in ascending numerical order (AMOS2 trial supplement).

What’s a typical digit span?

All three rows come from one research group, which used a calibrated, computerized version of the test and compared its results with the published WMS-III norms.

Group	Forward span	Backward span
Young adults, ages 18 to 46 (mean 26)	7.4	5.8
Community sample, ages 18 to 65 (mean 46.5)	6.4	4.6
WMS-III norms, age-matched to the community sample	6.6	4.9

Source: Woods et al., 2011.

Individual scores vary. Among the young adults, forward spans ranged from 5.7 to 9.0 digits (Woods et al., 2011). In the community sample, more years of education went with higher spans in both directions. Older age went with slightly lower backward spans, but forward span showed no significant link to age (same source).

Seven or four? Miller and Cowan

In 1956, Miller wrote that for many kinds of material, the span of immediate memory “is about seven items” (Miller, 1956). He also argued that the limit counts chunks rather than amounts of information, since the span stays nearly the same whether each item carries a little information or a lot (same source).

In 2001, Cowan revisited the question. He wrote that Miller’s seven was meant more as a rough estimate and a rhetorical device than as a real capacity limit. Pulling together a wide range of data, he argued for a central limit averaging about four chunks (Cowan, 2001). In a later summary, he put that limit at 3 to 5 meaningful items in young adults (Cowan, 2010).

People can still repeat about seven digits because ordinary span tests let them lean on other tricks. Cowan notes that you can keep about 2 seconds’ worth of speech going through silent rehearsal. When a task gets in the way of rehearsal, a smaller limit shows up. In “running span” tasks, where you don’t know when a list will end, people recall only the last 3 to 5 digits (Cowan, 2010). Psychologists Lisa Feigenson and Justin Halberda put it the same way: when measures are taken to block chunking, adults can store only three to four items (Feigenson & Halberda, 2008).

Why chunking helps

A chunk is a group of items that memory holds as one unit, like several words joined into a single image (Cowan, 2010). Feigenson and Halberda give an example: the letters PBSBBCCNN are much easier to recall once you see them as three TV networks, PBS, BBC and CNN (Feigenson & Halberda, 2008). They also point to the everyday habit of splitting phone, credit card and Social Security numbers into groups of two to four digits (same source).

Miller called this recoding. His example was regrouping 18 binary digits into 6 octal digits, which leaves far fewer chunks to remember (Miller, 1956). He thought we recode constantly in daily life, most often by translating things into words (same source).

Chunking can blur what a digit span test measures. In the Woods study, one participant used a mnemonic strategy, reached a backward span of 13 digits, and was dropped from the analysis (Woods et al., 2011).

Where digit span is used

• Digit span has been part of the Wechsler tests since the first version (Egeland et al.). It’s included in the Wechsler memory scales and the Wechsler intelligence scales for adults and children (Woods et al., 2011).
• In neuropsychological evaluations, Weintraub’s review of dementia workups lists Digit Span as a test of attention, specifically immediate span (Weintraub, 2022).
• For brief screening, the Montreal Cognitive Assessment (MoCA), a short test scored out of 30, includes forward and backward digit span items (Ang et al., 2023).

In those settings, a professional reads the score alongside other tests, education and history. A span you measure at home can’t diagnose anything.

Test yourself at home

You need a helper, or a list you recorded earlier and play back.

1. Write two random lists at each length, from 3 to 9 digits for forward and from 2 to 8 for backward, matching the WMS-III ranges (Woods et al., 2011). In their computerized version, Woods and colleagues kept neighboring digits out of runs like 1-2, 2-1 or 1-3 (same source). They also warn that familiar strings, such as your local area code, can inflate a score (same source).
2. Read at a steady pace. The study’s version played digits at one per second (Woods et al., 2011). Don’t group the digits with your voice, because that hands the listener free chunks.
3. Do forward span first. Start at three digits, two lists per length. Stop when you miss both lists at one length. Your forward span is the longest length you got right.
4. Then do backward span. Start at two digits and follow the same rule.
5. Keep the format the same. Hearing digits and seeing them can give different results, especially for backward span (Woods et al., 2011). If you retest, use the same method.

Compare your result with the table above, loosely. For a different kind of working-memory challenge, try the n-back test. If you’d rather measure how quickly you respond, see our guide to average reaction time.