Why is density considered a derived unit?

By derived unit, it means a quantity cannot be measured directly with any device (common lab instrument). One can't measure density of a substance with a rule, or scale, or bucket. read more

Derived units, sometimes called compound units, are different from base units because they are calculated from the base units mass and length. Density is one derived unit; force, area, volume, specific volume and mass fraction are also derived units. Each derived unit is defined by a quantity equation. read more

First of all density is a quantity, not a unit of any kind and definitely not a derived unit. In SI, the coherent unit of density is the kilogram per cubic meter (kg/m³), as density is mass divided by volume, mass has the base unit kilogram (kg) and volume is derived as the product of three mutually perpendicular lengths so its coherent unit is the cube of the base unit of length, the meter (m). read more

Density is a mass of a volume unit. A unit of density is defined as a unit of mass divided by unit of volume. In its turn, a unit of volume is a third degree of a unit of length. Mass and length units are main units. So density is a derived unit as derived from main units. read more