Carr index

The Carr index is an indication of the compressibility of a powder. It is calculated by the formula $C=100{\frac {V_{B}-V_{T}}{V_{B}}}$, where $V_{B}$ is the freely settled volume of a given mass of powder, and $V_{T}$ is the tapped density of the same mass of powder. It can also be expressed as $C=100\times (1-{\frac {\rho _{B}}{\rho _{T}}})$, where $\rho _{B}$ is the freely settled bulk density of the powder, and $\rho _{T}$ is the tapped density of the powder.

The Carr index is frequently used in pharmacology as an indication of the flowability of a powder. A Carr index greater than 16% is considered to be an indication of poor flowability.

The Carr index is related to the Hausner ratio, another indication of flowability, by the formula $C=100\times (H-1)$.

See also

Hausner ratio

References

Mark Gibson (2001). Pharmaceutical Preformulation and Formulation: A Practical Guide from Candidate Drug Selection to Commercial Dosage Form. Boca Raton: CRC Press. ISBN 1-57491-120-1.