Moisture Content

Moisture content (MC) is the weight of water in a piece of wood expressed as a percentage of the wood's fully dry weight, measured with a moisture meter (either pin-type, which reads resistance between two probes driven into the wood, or pinless, which reads capacitance through the surface). Freshly cut, green wood can run well over 30% MC; kiln-dried lumber is typically dried to somewhere around 6-8% for interior furniture use, matching the moisture content the wood will naturally settle back toward once it's living inside a heated or air-conditioned home.

It's the number that actually predicts a board's future behavior -- a board brought inside from an unconditioned garage or a lumberyard's non-climate-controlled storage can carry meaningfully higher MC than the room it's about to become furniture in, and building with it before it's acclimated is a common, avoidable cause of movement and joint failure after the fact. See the Wood Movement Estimator for how much dimensional change a given MC swing translates to.