Use a moisture meter Wood from the lumberyard is usually kiln dried. But how dry is it? It depends on how it was stored and for how long before you bought it.

These pinless moisture meters use flat plate electrodes that are placed on the surface of the wood to detect conductivity within the wood using electromagnetic waves.

Moisture in Wood: Meter Usage Helps Avoid Problems Whether you use a pin or pinless variety, moisture meters can help prevent warping and shrinkage in wood products.