A Census Bureau report says the American family has shrunk to its smallest size ever at 3.19 members, supporting previous studies that attribute the drop to a decline in births in the Baby Boom generation.

The report, released Wednesday, said that the 3.19-member family as of March 1987 contrasts with the 3.76-member family in 1940.In March 1986, the average family had 3.21 members.

Average household size also declined from 2.67 in March 1986 to 2.66 in March 1987 for an all-time low.

Population experts say the decline in births, known as the Baby Bust, has occurred as the millions of people born in the years following World War II pursued education and careers rather than immediately marrying and starting families.

Even though the total number of households has grown in recent years, the proportion maintained by married couples has declined, the study noted. In addition, those who do wed have tended to opt for fewer children, also helping lower the average family size.

The 1987 figures showed that the average family of 3.19 people included 0.96 under age 18 and 2.22 age 18 and over. The components don't add to 3.19 because of rounding.

By comparison, the average family included 3.76 people in 1940, of which 1.24 were under 18 and 2.52 were older.

Household size has declined additionally because of the growing number of one-person households in the country, population analysts say. Many of these are elderly people remaining on their own after the loss of a spouse, while others are young people on their own but not yet married.

Average family size is larger than that of households because households often contain only one person, while families by definition include at least two.

Here is a rundown of average family size in the United States since 1940:

Year Size

1987 3.19

1986 3.21

1985 3.23

1984 3.24

1983 3.26

1982 3.25

1981 3.27

1980 3.29

1975 3.42

1970 3.58

1965 3.70

1960 3.67

1955 3.59

1950 3.54

1940 3.76