250 units of weight per square
A stock pile is used to store large sized resources produced in a town. It stores logs, stone, iron, coal and firewood. Villagers harvesting or moving any of these resources will carry them to the closest stock pile with space available.
The largest possible stock pile size is 10x10. A single stock pile of this size, though, is rarely ever necessary.
Stock piles are constructed instantly, without a builder needed, unless the designated area needs to be cleared of resources beforehand. Villagers clearing the area for a new stock pile will carry the cleared raw materials to the closest other stock pile until the construction area is clear. Other clearable resources (i.e. gathering-related food or other resources left on the ground) will be carried to the closest available storage barn.
If you're building a stock pile close to an area you're clearing from resources, it is therefore recommended you try to place the stock pile where nothing will need to be cleared away beforehand, thereby making it instantly available.
Creating temporary stock piles near areas to be cleared helps laborers and villagers focus on clearing without the need for overly long trips. Areas will generally be cleared quicker. The temporary stock piles can later be deconstructed. to move the resources closer to town (just make sure no other temporary forward-stock pile is closer than your permanent ones, in which case you have to leapfrog it).
Villagers already carrying resources to a stock pile will NOT switch destination when a new closer stock pile pops into existence.
Before a stock pile is deconstructed, laborers will have to move any stocked resources elsewhere. It will not deconstruct and disappear until it is completely empty. An empty stock pile can be instantly removed without any villager/builder involvement.
If there are no other stock piles with available space on the map, deconstruction will halt and won't be completed until more storage space opens up somewhere.
If you have enough spare laborers to empty the deconstructing stock pile before all other stock piles fill up, they will go to their decided stock pile with the resources, and upon seeing it is full they will dump the carried resources on closest available ground.