It is named after the scientist Ralph J. Carr, Jr.
is the freely settled bulk density of the powder, and
The Carr index is frequently used in pharmaceutics as an indication of the compressibility of a powder.
On the other hand, in a poor-flowing powder where there are greater interparticle interactions, the difference between the bulk and tapped density observed would be greater, therefore, the Carr index would be larger.
[4] Another way to measure the flow of a powder is the Hausner ratio, which can be expressed as
Both the Hausner ratio and the Carr index are sometimes criticized, despite their relationships to flowability being established empirically, as not having a strong theoretical basis.
Use of these measures persists, however, because the equipment required to perform the analysis is relatively cheap and the technique is easy to learn.
Pharmaceutical Preformulation and Formulation: A Practical Guide from Candidate Drug Selection to Commercial Dosage Form.