Bulk and tapped densities are important physical parameters that influence the flow, compressibility, and packaging properties of pharmaceutical powders. Bulk Density is defined as the mass of powder divided by the bulk volume it occupies, including interparticle voids, without external compaction. Tapped Density is the mass of powder divided by the volume after being subjected to a standardized tapping process, which reduces interparticle voids.

The relationship between these densities provides a measure of powder flowability, as shown in the following formulas:
Hausner Ratio (HR) = Tapped Density / Bulk Density
Carr’s Index (CI) = [(Tapped Density - Bulk Density) / Tapped Density] × 100

Lower Hausner ratio and Carr’s index values indicate better flow properties. These parameters are widely used in pharmaceutical quality control and process design.