The way I understand the word "density" to be used is as if a space is filled by infinitesimally small objects--points. However, in my usage, I'm looking for a word that signifies that a certain percentage of space is occupied by objects.

To illustrate, consider a space of a given volume, containing a given number of spheres. Compare this with a space that has twice the volume and contains the same number of spheres but each now also has twice the volume. "Density", as the number of objects per unit of volume, is now half. But "occupancy", as the fraction of space occupied by the spheres, is the same in both cases.

What is a good word for this "occupancy" measure?

2 Answers 2


Its called packing density

Packing Density
The fraction eta of a volume filled by a given collection of solids.

Weisstein, Eric W. "Packing Density." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/PackingDensity.html

  • Thank you, that looks like its very close. One further twist I just realized when i examined your answer. I am not talking about densely packed spaces, it could be just a few marbles in a room (hah, this is starting to sound like a funky picture). Taking the definition of packing density literally, all is fine. But i wonder about the associations this may conjure up. Commented Apr 26, 2016 at 7:08

Density is almost always mass density, the mass per unit volume. If you want to clearly differentiate, the usual solution is a qualifier word. What you are talking about sounds like number density, the number of objects per unit volume.

  • Thank you! This is not the most intuitive term, but i see from the wikipedia page that it does look like it has the correct meaning. Commented Apr 26, 2016 at 7:09

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