Hausner’s Ratio

Hausner’s ratio, also known as the Carr’s compressibility index, is a measure used in the pharmaceutical industry to assess the flowability and compressibility of powders and granular materials. It is a simple way to predict how well a powder will flow and how easily it can be compressed into tablets or other solid dosage forms.

Hausner’s ratio is calculated using the following formula:

Hausner’s Ratio = (Bulk Density / Tapped Density)


Bulk Density: The bulk density of a powder is the ratio of the mass of the powder to its bulk volume. It is typically measured by pouring the powder into a graduated cylinder and recording the volume it occupies.

Tapped Density: The tapped density of a powder is the ratio of the mass of the powder to its tapped volume. Tapped density is determined by mechanically tapping the container holding the powder until there is no further volume reduction.

The Hausner’s ratio provides an indication of the flowability of the powder. Generally, lower values of Hausner’s ratio indicate better flow properties. Here is a rough interpretation of Hausner’s ratios:

 Flowability Scale 
Compressibility IndexFlow CharacterHausner Ratio
<10Excellent1.00 – 1.11
11 – 15Good1.12 – 1.18
16 – 20Fair1.19 – 1.25
21 – 25Passable1.26 – 1.34
26 – 31Poor1.35 – 1.45
32 – 37Very Poor1.46 – 1.59
>38Very Very Poor>1.60

Flowability Scale

Pharmaceutical manufacturers use Hausner’s ratio and related flowability measurements to optimize the formulation and processing of powders for tablet production and other dosage forms. Powders with poor flow properties may require modifications to their composition or processing conditions to improve flowability and ensure consistent tablet quality.

Also read: Angle of repose

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