To envision porosity,
look at the picture on the bottom left. If the solid portion
of the soil could be completely compacted, so all the air and
water
were
squeezed out of it, it would have zero porosity. In this
case, one cubic meter of soil contains 0.7 cubic meters of soil
particles, and therefore 0.3 cubic meters are occupied by either
water or air (voids). Porosity can then be calculated
with this equation:

Porosity = void volume ÷ soil volume

Porosity = 0.3 cubic meters ÷ 1.0 cubic
meters

Porosity = 0.3