In freshly cut wood (green wood), both the cell walls and the lumina (empty spaces) are saturated with water. The moisture content of greenwood is higher in the sapwood than in the heartwood and ranges from ~50% (maple heartwood) to >150% (spruce sapwood).
During the seasoning process the moisture content of the wood is gradually reduced until no free (e.g. luminal water) is present and water bound to the structures/fibers of the wood is in an equilibrium with the moisture of the surrounding air. This process takes years, and its duration depends on the wood species as well as the shape/thickness of the respective piece of wood. Our suppliers are experts in this seasoning process, which involves the storage of wood both outdoors and indoors.
When the wood arrives at our company, we store it indoors under temperature and humidity controlled conditions(~70°F; ~45%-50%). Over time, the wood will equilibrate with the moisture in the air resulting in an EMC (equilibrium moisture content) of 8-10%. We measure the moisture content of our wood using a pin-less moisture meter from Wagner Meters (USA).
Please note that the EMC of the wood (and its weight and dimensions) may change depending on the environmental conditions in your workshop.