Bulk density is a measure of the weight of dry soil in a given volume. The soil volume is the combined volume of solids and pores, which may contain air and/or water.
A bulk density sample is taken by inserting a ring (cylinder) of known volume into the soil, then carefully excavating to remove both the ring and the soil it contains.
Soil is dried and weighed. The bulk density of the soil (g/cm3) is equal to the dry weight of soil (g) divided by the soil volume (volume of the ring) (cm3).