Family size may be considered from two perspectives. At the individual (micro) level, it defines one aspect of an individual's family background or environment. As such, it represents a potential influence on the development and accomplishments of family members. At the societal (macro) level, family size is an indicator of societal structure that may vary over time, with concomitant implications for individual development and social relations in different cohorts. In this essay, consideration is given to both aspects of family size, as it is reflected in sociological theory and research.

While the term family size is sometimes used to represent the total number of individuals comprising a family unit, Treas (1981) argues convincingly for decomposing the concept into two components: numbers of children and numbers of adults in the household. This distinction is important, as observed patterns of change in overall family size may be attributable to...