Get Carr's Index and Hausner ratio to assess powder flow from bulk and tapped volumes.
Bulk and tapped density testing predicts how a powder will behave during handling, hopper flow, and compression — long before it reaches a tablet press. Weigh a powder sample, measure the volume it occupies loosely in a graduated cylinder, then measure it again after a set number of mechanical taps, commonly following the method described in USP <616>.
From those two volumes, this calculator works out Carr's Index and the Hausner ratio — the two most commonly referenced measures of powder flowability, useful early in formulation development when comparing how different diluents, granulation methods, or lubricant levels affect flow.
A poor result here is often the first sign a formulation will need adjusting before it reaches full-scale production — catching it on the bench avoids costly downtime from hopper bridging or inconsistent die fill later.
Generally, values below 15% suggest good flow, while values above 25% suggest poor flow that may need formulation changes.
Bulk density is measured before any mechanical tapping; tapped density is measured after tapping compacts the powder into a smaller volume.
Read the full article: Carr's Index & Hausner Ratio Explained →