Volumetric soil moisture is more comparable than gravimetric soil moisture because the density of soil can vary widely. Also, volumetric soil moisture better reflects a volume of water that would be applied by an irrigation cycle, thus, soil moisture is expressed as a volumetric water fraction or volumetric percent. The soil water fraction by volume is;

θ = ^V_w/_Vtot     [1]

Where the Greek letter theta, is the symbol used for volumetric soil moisture, V_w is the volume of water in a sample and V_tot is the total volume of the sample. Because one gram of water is basically equal to one cubic centimeter which is equal to one milliliter, grams of water can be used in equation [1] for determining V_w. V_w is determined from the weight of the wet soil minis the weight of the soil after drying in the oven.

V_w = (Weight of Wet Soil) – (Weight of Oven Dry Soil)     [2]

The wet soil, however, cannot be weighed on a balance without the apparatus so the wet weight of the soil is;

Weight of Wet Soil = (Total Weight of Apparatus holding the wet soil) – (Weight of the Apparatus) – (Weight of Dry Soil)     [3]

The weight of the dry soil is determined by drying the soil sample for 24 hours at 100 degrees C.

The stand and the water line connectors included in the kit, ensure an accurate weight of the wet soil on a balance. The weight of  the stand, the probe, and the assembly are known and can be subtracted from the total weight of the wet soil, equation [3].

Soil needs to be wetted from the bottom so that all of the air gets pushed out the top. A reservoir and high-quality hoses are included to push water into soil sample from the bottom. A stainless-steel ring with a known volume of 401 cc (V_tot) and with screen mesh is included. The stand allows for the whole apparatus to be placed on a balance.