As far as we can tell, Medieval French families were significantly bigger than modern western families - averaging perhaps around five to six. In contrast, modern France has an average household size of 2.38. However, they remained relatively small scale, and somewhat nuclear families of mostly two generations. Note the standard disclaimers apply: pre-modern demographic statistics are extremely patchy, and often must be interpreted with laborious reconstructions.
Nonetheless, the earliest available information on this subject probably dates to about the 8th Century. Around this time, surveys of estates began to appear that documented - with varying completeness - the households living off those lands. Of the surviving records from Medieval France, the largest and most famous is probably the Polyptych of Irminon, a survey of almost 2,000 properties in Saint-Germain-des-Prés.
Conducted by the Abbot of the eponymous abbey in the early 9th Century, it contained 1,742 households with over 8,600 inhabitants between them. Analysis of the Polyptych produces the following breakdown:
From this, the late David Herlihy calculated that:
The average size of the households on the lands of St. Germain is 5.75 persons, and the median size is 6.
- Herlihy, David. Medieval Households. Harvard University Press, 1985.
A feature of medieval household sizes in Western Europe was that well-off families were larger than poorer families. This trend is illustrated in the above graph, where average household sizes nearly doubled as the amount of arable land in the estates they lived on went from lowest the highest. To some degree this would have been due to the need for additional manpower on larger estates, but it is also a reflection of wealthier families' ability to support more offspring through infancy and childhood. This contrasts with modern families, where the more well off tended to have less children.
In addition, the survey also revealed that the households at St Germain were predominantly laterally extended families. That is, there were more people from the same generation living together, as opposed to having more generations in the same household. Instead of grandparents living with their children and grandchildren, St Germain families were more commonly consisted of siblings and their children. A related feature is that, despite a somewhat high family size, the number of children was low - perhaps a product of late marriages.
"There is very little evidence of vertical extension, that is, over generations. There are only 26 grandmothers among the 3,470 women, and no grandfathers ... The absence of [the] three generational families, and of grandfathers, grandmothers and grandchildren, is thus striking.
- Herlihy, David. Medieval Households. Harvard University Press, 1985.
This situation can be contrasted In Southern France, where the stem family system eventually developed during the Late Middle Ages. That pattern became predominant by the onset of the Early Modern period.
In northern France simple families predominated, but starting in 1350 stem and joint families appeared to be more common in Languedoc and southern France.
Nicholas, David. "The Ties That Bound: Peasant Families in Medieval England." (1987).
