Grain water content refers to the percentage of free water and bound water in grain. Under a certain temperature and humidity condition, after moisture absorption and moisture dissipation, the water vapor pressure in the grain pile and the water vapor pressure outside the grain pile reach equilibrium, and the moisture of grain and oil at this time is the equilibrium moisture under this temperature and humidity condition.

The equilibrium moisture of grain is closely related to the stability of stored grain. Generally speaking, the moisture content in balance with 75% relative humidity is the maximum safe moisture for short-term storage. The water content in balance with 65% relative humidity is the maximum safe humidity for long-term storage. By judging the changing trend of equilibrium moisture, the timing of ventilation and sealing can be determined.