The following terms are commonly used to describe how soil moisture is quantified: 

• Soil water content is a measurement of the amount of water in a known amount of soil; it can be expressed as % water by weight or volume of soil, or inches of water per foot of soil.
• Soil water potential or soil moisture tension is a measurement of how tightly water clings to the soil and is expressed in units of pressure called bars (one bar is equal in strength to the pressure of one atmosphere). Generally the drier the soil, the greater the soil water potential and the harder a plant must work to draw water from the soil.
• Plant available water (PAW) is the amount of water in the soil between the soil’s field capacity (soil water content after gravity has removed any freely draining, excess water) and its permanent wilting point (soil water content at which most plants can not recover from wilting). It is expressed as inches of available water per foot of soil.