Void ratio (e) is the ratio of the volume of voids (V_v) to the volume of soil solids (V_s), and is expressed as a decimal. The void ratio is always greater than zero, in some cases, it may have a value greater than 1. Coarse grain soil has a smaller void ratio as compared with fine grain soils.

When spherical grains are arranged in a cubical array, the maximum possible void ratio is 0.91. Similarly, when arranged diagonally the least void ratio is 0.35

Porosity (n) is the ratio of the volume of voids to the total volume of soil (V ), and is expressed as a percentage. The value of porosity lies between 0 to 100%. The relationship between void ratio and porosity can be expressed as below.

Degree of saturation (S) is the ratio of the volume of water (Vw) to the volume of voids (Vv). This value represents the amount of water as compared with the amount of voids. The value of S ranges from 0 (Dry soil) to 100 %. Soil with S= 100% is known as fully saturated soil.

Air Content (ac) is the ratio of the volume of air (Va) to the volume of voids (Vv). For fully saturated soil ac = 0 and dry soil ac = 100 %.

Percentage air voids (na) is the ratio of the volume of air (Va) to the total volume of soil.(V). The relationship between % air voids and Air content can be expressed as below