Basic Soil and Water Relations

In a soil system of total volume Vtotal and total weight or mass Wtotal:

Vtotal = Vair + Vwater + Vsolid                                           ...(eqn. 1)
Vvoid = Vair + Vwater                                                         ...(eqn. 2)

Wtotal = Wair + Wwater + Wsolid                                       ...(eqn. 3)

Equations 1 and 3 state that the total volume or weight of a soil is the total of the space occupied by air, water, and solid.

Meanwhile, you can find the volume of void space by equation 2. Void space is the space that is not occupied by any solid matter.