Final answer:
Density is commonly measured in kilograms per cubic meter (kg/m³) in the SI system, but often expressed as grams per cubic centimeter (g/cm³) in laboratory settings for convenience, especially since water has a density of 1 g/cm³.
Step-by-step explanation:
The SI units for density are expressed as kilograms per cubic meter (kg/m³). This is because kilograms (kg) are the SI units for mass, and meters (m) are the SI units for length. However, in many practical situations, such as in a laboratory, density is more commonly expressed in grams per cubic centimeter (g/cm³) because this unit is more convenient for most solids and liquids.
For example, the density of water is about 1 g/cm³, which is equivalent to 1000 kg/m³, aligning with the historical metric system design. Furthermore, for substances with lower density like gases, density might be reported in grams per liter (g/L).