Density

Density is a measure of mass per volume. In SI density is measured as kg m^-3 (kilograms per cubic metre), but many people use the more convenient g cm^-3 (grams per cubic centimetre) or (equivalently) kg l^-1 (kilograms per litre). The higher density, the higher mass per volume.

Formerly mass and volume were linked by defining the gram to be the mass of one cubic centimetre of water which meant that water had density 1 kg/litre. Now length (that is the metre), and hence volume, and mass (that is the kilogram), are defined independently of water so the density of water is not quite exactly 1 but it is still very close. A cubic metre of water thus weighs a ton.

1000 kg m^-3 is 1 g cm^-3.

The perhaps highest density known is reached in neutron star matter. A black hole, according to current theories, does not have any volume, and its density can be seen as either infinite or non-existent.

The densest naturally occurring substance on Earth is osmium, its density is about 22 kg/litre.

This use of density is also known (if you follow [ISO 31]?) as volumic mass (that is, mass divided by volume).

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Density may denote how much of a certain substance, object or occurrance is present within a certain area or volume. Often used is population density, meaning how many people on average live in an area (usually persons per square kilometre).

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