A sequence of digits will flash on screen. Repeat them back in the same order (Forward), or in reverse (Backward). Used in standardized IQ assessments worldwide.
The Digit Span subtest is part of the Wechsler Adult Intelligence Scale (WAIS-IV) and other major IQ batteries. Forward span tests simple verbal working memory; backward span tests active manipulation of information — a stronger predictor of fluid intelligence.
Average forward span is 7 digits, backward span is 5 digits. For related tests, try Number Memory and N-Back.
Digit Span has been part of formal intelligence assessment since David Wechsler's original 1939 scale. It remains a core subtest of the WAIS-IV (for adults) and WISC-V (for children) today — over 80 years of continuous clinical use. The test exists in two conditions: Forward Span (repeat digits in the same order) and Backward Span (repeat digits in reverse). These measure fundamentally different cognitive operations.
Forward span tests passive verbal storage capacity — holding a sequence in phonological working memory. Backward span tests active manipulation — you must mentally reverse the sequence while holding it, engaging executive control and mental transformation processes. Backward span is a stronger predictor of fluid intelligence and correlates more highly with complex reasoning performance. Average forward span is 7 digits; average backward span is 5 digits.
A large gap between forward and backward span (e.g., 9 forward but only 4 backward) suggests strong phonological memory storage but limited active manipulation — which can predict difficulty with complex mental arithmetic or multi-step reasoning tasks. A small gap indicates that your manipulation and storage capacities are well-matched.