A unit of measurement describes one unit of a quantity. Units of measurement can be imperial or metric. They can be converted using conversion factors.
Density is a measure of how compact an object is. It is a measurement of the amount of a substance contained in a certain volumeThe volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml.. For example, the density of a cloud is much less than the density of a gold bar.
The density of any solid is the mass of the object divided by its volume.