Bulk density a property of particulate materials. It is the mass of many particles of the material divided by the volume they occupy. The volume includes the space between particles as well as the space inside the pores of individual particles.

Bulk density is not an intrinsic property of a material; it can change depending on how the material is handled. For example, grain poured in cylinder will have a particular bulk density; if the cylinder is disturbed, the grain particles will move and settle closer together, resulting in a higher bulk density. For this reason, the bulk density of powders is usually reported both as “freely settled” and “tapped” density (where the tapped density refers to the bulk density of the powder after a specified compaction process, usually involving vibration of the container.)