Acre - "The amount of land which one team can plough in a day. 120 [acres] was the average to maintain one family but this varied depending on the land." (From: http://thescriptorium.co.uk/glossary.php)
Today we measure an acre as "a common variable unit of land measure, now equal in the U.S. and Great Britain to 43,560 square feet or 1 / 640 square mile (4047 square meters)." (http://dictionary.reference.com/browse/acre)
I wonder how many acres would sustain a single family today.
What do you think?