How big should farms be?

[Gandwarf]

http://www.hyw.com/books/history/Agricult.htm

Two interesting parts of this text:

1. In England, the ideal farm size for a family was a "yardland" (24-30 acres) in size. Only about a quarter of the English farm families had this much land (or a bit more) before the Bubonic Plague , most had ten or fewer. Those farmers possessing a yardland were able to work their land efficiently enough to feed themselves and produce a surplus for sale.

2. An acre of barley could, in an average year, produce about 500 liters of grain (after making allowances for taxes and seed for the next crop). This was enough to feed one adult for a year at a very basic level. A farmer with a wife and two children could get along with five acres. Everyone would have to work, especially for other sources of food like the vegetable garden and rummaging in the woods for mushrooms, nuts, and berries. But a five acre holding left little margin for bad weather. Several bad years in succession could lead to widespread famine.