Bulk and Tapped Density

Tapped density testing is the flowability study of "tapping down” a powder to determine how much it settles during transit.

Measuring the powder density once it’s been tapped allows for precise measurement and helps determine the most suitable packaging of the product.This technique is useful for all types of powders and granules, from pharmaceuticals to washing powder.We usually tap the powder for 100 cycles, for example using a Copley Tapped Density Tester.

Copley Tapped Density

Using the Copley Tapped Density Tester, the powder is mechanically tapped inside a cylinder until there is no change in the volume of the product.

A Copley Tapped Density Tester allows us to work out the tapped density (in grams per ml). To do this, we divide the weight of the sample by the final tapped volume. Using these figures, we are then able to calculate the compressibility index and Hausner ratio to assess the products’ ability to settle.

Compressibility Index calculation (also known as Carr’s Index):

C = 100x (1 – Bulk Density / Tapped Density)

Hausner Ratio calculation:

H = Tapped Density / Bulk Density

Using the two calculations above, we can provide an assessment of the flow character of the powder.


 Compressibility Index  Flow Character  Hausner Ratio
 1 to 10%  Excellent  1.00 to 1.11
 11 to 15%  Good  1.12 to 1.18
 16 to 20%  Fair  1.19 to 1.25
 21 to 25%   Passable   1.36 to 1.34
 26 to 31%   Poor  1.35 to 1.45
 32 to 37%  Very Poor  1.46 to 1.59
 38% and above  Very, Very Poor  1.60 and above

Carr, R L. Evaluating flow properties of solids.Chem Eng 1965; 72:163-168.

For more information about bulk and tapped density, get in touch today by completing our online contact form here, or by emailing info@merlin-pc.com, or by calling +44(0)1509 860 222.


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