Declines in Household Size & Ramifications for Growth

Persons per household (PpH), a measure of average household size, is calculated by dividing the number of  people living in households  by the number of  occupied housing units .

Higher PpH is generally associated with  neighborhoods  with larger housing units, more family households, and higher birth rates, while lower levels of PpH are usually found in more affluent and in aging neighborhoods. When neighborhood characteristics change, these are often reflected in shifts in average household size. When PpH increases, the existing housing stock accommodates more people. A declining average household size, on the other hand, means that the population is “spreading out” across housing units, and more housing is needed to maintain the original population size. By the same token, a neighborhood’s declining PpH dampens the effects of new construction on population growth, since a portion of new units is needed to offset that decline. Indeed, in neighborhoods with steep declines in PpH, increases in housing units are sometimes barely sufficient to maintain the initial population.

Over the last decade New York City’s PpH declined by 0.02, continuing a long-term trend of declining average household size. At the same time, New York City’s population is projected to increase in the coming decades. Thus, housing units will need to be produced to accommodate both the growing population and offset the smaller number of people in each household.

This report first examines neighborhood PpH in 2020 and changes in PpH from 2010, which were not even across the city’s neighborhoods. It then focuses on those neighborhoods with declining PpH and analyzes the ramifications of these declines for population growth.

The total population includes those living in households as well as those living in group quarters, which include facilities such as college residence halls, residential treatment centers, correctional facilities, or military barracks. Unless otherwise noted, references to population refer to the household population.

The overall housing stock includes both occupied and vacant housing. Housing is considered vacant if there is no occupant, or if the unit is not a primary residence, such as a pied-à-terre. Persons per household is derived from occupied units.

Throughout this report, the term “neighborhood” is used synonymously with Neighborhood Tabulation Areas (NTA). NTAs are medium-sized statistical geographies that roughly approximate New York City neighborhoods for the purpose of reporting Decennial Census and American Community Survey (ACS) data. NTAs are created by aggregating census tracts and nest within Community District Tabulation Areas (CDTA). For more information on 2020 NTAs, and changes from 2010, see  2020 Census Reconfiguration of Statistical Geographies .

Growth in the housing stock between 2010 and 2020 reflects net additions through new construction, demolitions, alterations, as well as the creation of informal units. This growth can be accurately captured in census data only if the decennial census accurately enumerates the housing stock at both points in time. The Census Bureau  partnered with New York City  to ensure that it had the address of every housing unit in the city.