Untapped bulk density

What is Untapped bulk density and How to measure Untapped bulk density ?

Bulk density refers to the mass of a material per unit volume when it is loosely packed. It is commonly used to measure the density of granular or powdered substances. Bulk density is typically expressed in units such as kilograms per cubic meter (kg/m³) or grams per cubic centimeter (g/cm³). By determining the bulk density of a material, it becomes possible to estimate its weight or volume in different scenarios, such as storage, transportation, or manufacturing processes.

The determination of the untapped bulk density of a powder can be performed using three distinct methods:

  • Method 1, which involves measuring the volume of a known mass of powder in a graduated cylinder;
  • Method 2, which requires measuring the mass of a known volume of powder passed through a volumeter into a cup; and
  • Method 3, which entails measuring the mass of a known volume of powder introduced into a measuring vessel.



  1. Begin by passing a sufficient quantity of the powder sample through a sieve with apertures equal to or greater than 1.0 mm. This step aims to break up any agglomerates that may have formed during storage. Handle the powder gently during sieving to preserve its original characteristics.
  2. Weigh approximately 100 g (m) of the test sample with an accuracy of 0.1%. Use a dry graduated cylinder with a capacity of 250 mL (readable to 2 mL).
  3. Take care to avoid significant compacting stress while pouring the powder into the cylinder. You can use a funnel or tilt the cylinder to facilitate the process without exerting excessive force.
  4. If necessary, level the powder carefully without compacting it. Then, read the untapped bulk volume (V0) to the nearest graduated unit.
  5. Calculate the untapped bulk density in grams per milliliter using the formula m/V0. For accurate results, it is advisable to perform replicate determinations.
  6. If the untapped bulk volume falls outside the range of 150 mL to 250 mL (more than 250 mL or less than 150 mL), adjust the amount of powder sample accordingly. The untapped bulk volume should be greater than or equal to 60% of the total volume of the cylinder. In the expression of results, specify the mass of the test sample.

Note: If the untapped bulk volume ranges from 50 mL to 100 mL, a 100 mL cylinder readable to 1 mL can be used. In such cases, include the volume of the cylinder in the expression of results.

Method 2: Measurement in a Volumeter of Untapped bulk density


The apparatus (Figure 1) comprises a top funnel equipped with a 1.0 mm sieve, a baffle box containing four glass baffles, and a cup positioned directly beneath the baffle box. The cup can either be cylindrical, with a volume of 25.00 ± 0.05 mL and an internal diameter of 29.50 ± 2.50 mm, or cubical, with a volume of 16.39 ± 0.05 mL.

Volumeter of Untapped bulk density

Note: The apparatus (the Scott Volumeter) conforms to the dimensions in ISO 3923-2:1981 or ASTM B329-14.


  1. Allow an excess amount of powder to flow through the apparatus into the sample receiving cup until it overflows. Use a minimum of 25 cm³ of powder for the cubical cup and 35 cm³ for the cylindrical cup.
  2. Carefully remove any excess powder from the top surface of the cup. To achieve this, smoothly move the edge of a reclined spatula blade across the cup’s top surface. Tilt the spatula backward to prevent packing or unintentional removal of powder from the cup.
  3. Determine the mass (m) of the powder to the nearest 0.1%. Record the average of three determinations using three different powder samples.
  4. Calculate the untapped bulk density in grams per milliliter using the formula m/V0, where V0 represents the volume of the cup.
Scott Volumeter

Method 3: Measurement in a Vessel


The apparatus consists of a 100 mL stainless steel cylindrical vessel with dimensions as specified in Figure 2.

Measurement of Untapped Density by Measurement in a Vessel


  1. Pass a sufficient quantity of the powder sample through a 1.0 mm sieve, if required, to break up any agglomerates that may have formed during storage.
  2. Allow the obtained sample to flow freely into the measuring vessel until it overflows.
  3. Carefully remove any excess powder from the top of the vessel, following the same procedure described in Method 2.
  4. Determine the mass (m0) of the powder to the nearest 0.1% by subtracting the previously determined mass of the empty measuring vessel.
  5. Calculate the untapped bulk density in grams per milliliter using the formula m0/100.

Use of Untapped bulk density

  1. Powder Flowability: Untapped bulk density provides valuable information about the flow properties of powders. Materials with high untapped bulk density tend to have poor flowability and may exhibit issues such as arching, rat-holing, or bridging in hoppers, silos, or conveying systems. This measurement helps engineers and manufacturers assess and improve powder flow characteristics, ensuring efficient and reliable material handling processes.
  2. Packaging and Transportation: Untapped bulk density is considered when determining the amount of material that can be accommodated in a given volume or container. Packaging and transportation decisions rely on accurate measurements of bulk density to optimize space utilization, reduce packaging costs, and minimize transportation expenses.
  3. Quality Control: Untapped bulk density is often used as a quality control parameter to monitor the consistency of powdered or granular products. By establishing acceptable ranges of bulk density, manufacturers can ensure that their products meet desired specifications. Deviations from the expected untapped bulk density may indicate variations in particle size, moisture content, or other properties that can affect product performance.
  4. Formulation Development: In industries like pharmaceuticals and food processing, untapped bulk density is used during the formulation development stage. It helps scientists and researchers optimize the composition and processing conditions of powdered or granular formulations. By manipulating the untapped bulk density, they can achieve desired characteristics such as improved tablet compressibility, enhanced dissolution rates, or controlled release profiles.
  5. Powder Characterization: Untapped bulk density is one of the parameters used to characterize and classify powders according to international standards such as the Unified Soil Classification System (USCS) or the Geldart Powder Classification. These classifications assist in understanding the behavior of powders in different processes and aid in the selection of appropriate equipment and handling methods.

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