Bulk density: fill the powder sample into a measuring cup, flatten the top, the ratio of the powder mass to the volume of the cup is defined as bulk density. It indicates the mass of the powder that can be added into the vessel per volume under the normal conditions.
Tap density measurement
: fill the powder sample into a measuring cup; vibrate the cup at certain amplitude and frequency to remove air from the powders. After reaching the required vibration time, flatten the sample. The ratio of the powder mass to the volume of the cup is defined as tap density. Tap density indicates the mass of powders filled into the vessel per volume after excluding air from the powders. The data of bulk density and tap density are often used for the design of vessels, bags, and tanks for powder storage.
Compression ratio: it is the ratio of the difference between tap density and bulk density to tap density. It shows the degree of volume reduction from bulk to tap state.