Is working memory related to IQ?

The short answer

Working memory and fluid IQ (the ability to solve novel problems) correlate strongly — typically r ≈ 0.5–0.6 in meta-analyses. This is one of the highest correlations between any cognitive test and general intelligence.

The relationship is not simply that smart people have better memory — it is that working memory capacity is a core component of fluid intelligence. It limits how many variables you can hold in mind simultaneously when solving a problem, which directly constrains reasoning complexity.

The correlation looks even stronger when researchers use latent-variable methods, which combine several memory tasks to strip out task-specific noise: there, working memory capacity and fluid intelligence (Gf) typically correlate around 0.6-0.7. The leading explanation is shared machinery - both abilities depend on controlled attention and on the same prefrontal-parietal networks that keep goals active in mind while resisting distraction.

The data

What it means for you

A strong correlation does not mean the two are the same thing. Working memory and fluid intelligence are statistically separable constructs, and the clearest demonstration is the transfer problem: intensive working memory training reliably improves the trained tasks, yet it does not raise IQ - a result replicated across multiple large trials and a central finding of the brain training literature. If working memory capacity were simply intelligence under another name, training one would lift the other.

Task choice also matters when interpreting your own scores. Simple span tasks such as forward digit span - pure storage, nothing else - correlate with IQ comparatively weakly. Complex span tasks, which force you to hold items in mind while doing something else (solving sums between the letters you must remember, for example), correlate substantially more strongly, because they tax the controlled-attention component that overlaps with reasoning. So a strong digit span result reflects phonological storage more than it reflects reasoning ability.