The psychometric approach considers intelligence as aggregate of abilities. It expresses the individual's performance in terms of the single index of cognitive abilities. The psychometric approaches to intelligence lay emphasis on studying intelligence as a constellation of abilities, expressed in a quantitative term such as IQ.

Two theories based on this Approach:
UNI/One Factor Theory (Alfred Binet): The ability to judge well, understand well and reason well.
Differentiating more intelligent from less intelligent individuals.
Conceptualised intelligence as consisting of one similar set of abilities which can be used for solving any or every problem in an individual's environment.

Two-factor theory (Charles Spearman), 1927: Employed a statistical method called factor analysis.
(ii)Intelligence consists of a general factor (a) G-factor and specific factor (b) S-factor.
(a) G-Factor: It includes mental operations which are primary and common to all performances.
(b) S-Factor: It includes specific abilities which allow individuals to excel in their respective domains.