The mass density or density of a material is its mass per unit volume.
Applicable units are those of quantitykind:MassDensity
http://en.wikipedia.org/wiki/Density
https://cdd.iec.ch/cdd/iec61987/iec61987.nsf/ListsOfUnitsAllVersions/0112-2---62720%23UAD106
The mass density or density of a material is its mass per unit volume.
$\rho = \frac{dm}{dV}$, where $m$ is mass and $V$ is volume.
http://www.iso.org/iso/catalogue_detail?csnumber=31894
http://www.iso.org/iso/catalogue_detail?csnumber=31889