Hausnerratio

The Hausner ratio is a dimensionless parameter used in powder technology to evaluate the flowability of powders. It is defined as the ratio of tapped density to bulk density. Bulk density is the mass of powder divided by its untapped volume, while tapped density is the mass divided by the volume after a standardized tapping sequence. In practice, a simple tapping device or a densimeter with a fixed number of taps is used to obtain the tapped density.

The ratio is calculated as Hausner ratio = tapped density / bulk density. Values close to 1.0 indicate free-flowing powders, while higher values indicate increasing cohesion and poorer flow. Typical interpretation ranges are approximately less than 1.25 for good or free-flowing powder; 1.25–1.50 for medium to poor flow; and above 1.50 for very poor flow. Exact thresholds vary by material and measurement method.

The Hausner ratio is widely used in pharmaceutical and chemical industries to predict handling properties during manufacturing and storage, for example in hopper design, tablet compression, and granulation processes. It is often considered alongside the Carr compressibility index, which is derived from the same densities and provides a related measure of powder compressibility.

Limitations: results depend on measurement conditions, including tapping amplitude, equipment, sample preparation, and humidity. The ratio reflects interparticle cohesion and packing efficiency, and does not capture all aspects of flow such as aeration or dynamic behavior under process conditions. Nonetheless, the Hausner ratio offers a quick, non-destructive indicator of powder flow behavior useful in formulation and process development.