The soil bulk density, also known as dry bulk density, is the weight of dry soil divided by total soil volume. The total soil volume is the combined volume of solids and pores which may contain air or water, or both. The average values of air, water and solid in soil are readily measured and are a useful indication of a soils physical condition.

Bulk density is most commonly used in agriculture when investigating compaction layers which occur between 10?40 cm as a result of machinery and stock impacts. This simple measurement can also be used to determine various nutrient levels and other soil quality indicators on an area basis, by converting weight measurements (e.g. mg/kg) to area measurements (e.g. kg/ha). Bulk density is necessary for calculating carbon stocks (sequestration) from carbon percentage (see Total Organic Carbon factsheet).