The average household of 5 survives on 1 sp per day. This provides bread, cheese, milk, eggs, ale or wine, firewood, and leaves a little left over each week for buying cloth, salt, honey, meat, or other luxury items. It also covers taxes.
1 sp a day for 6 days a week(nobody works on sundays!) equals out to 312 sp per year, or 3120 cp.
In my campaigns I also usually introduce half-pieces(hp), which are worth 1/2 a cp, for a total of 6240 distinct units of currency available to a family of 5 each year. However, for purposes of this article, I will stick with cp.
From this information, we can figure that the average person requires 624 cp to have an "average" lifestyle.
We're also assuming that it takes 5 acres to support a single individual in a similar fashion(2 acres crop, 2 acres pasture, 1 acre other(stuff to be replanted the following year, winter feed, etc). As such, we can assume that 5 acres will generate 624 cp a year in terms of goods, or roughly 125(124.8) cp a year per acre.(Note: I could go a lot more detailed on how to generate a village farm is run, but frankly, Harn-Manor has already done that, and I'd just be ripping them off).
After figuring out how much your farmers produce and consume, you'll be able to figure out how much actual surplus they have. This surplus may be used to feed/clothe towns and cities.
Next time; How to generate production!