Powder mass divided by its occupied bulk volume, including spaces between particles.
Also called: poured density; apparent bulk density.
What volume does bulk density include?
Bulk density includes the spaces between particles. In a poured powder measurement, the occupied bed volume includes those spaces as well as the particles themselves. A result therefore describes a powder in a particular packing state, rather than just the density of its solid material.
Skeletal and true density use different volume definitions. A gas-pycnometer value and a poured bulk-density value should not be treated as interchangeable entries in a capsule-capacity calculation. Also check the word “apparent”: terminology varies, so the reported method matters more than that label alone.
Bulk-density formula and unit conversion
Divide sample mass by the bulk volume measured in the stated condition. Keep the units visible; g/mL and g/cm³ have the same numerical value, whereas conversion to kg/m³ changes the number.
First establish whether both results are poured values. A tapped result describes a different packing history. Then compare sample preparation, loading method, container and volume-reading basis before attributing the difference to a changed formulation.
A useful comparison retains the powder identity, measurement method, sample condition and units beside the value. Bulk density alone does not identify particle density, explain every flow problem or establish the density achieved by a dosing system.