The most common unit for density in science is kilograms per cubic meter, written as kg/m3\text{kg/m}^3kg/m3.

Core idea

Density measures how much mass there is in a certain volume, using the formula
ρ=mV\rho =\dfrac{m}{V}ρ=Vm​, where mmm is mass and VVV is volume.

Because it is “mass per unit volume,” any density unit is a mass unit divided by a volume unit.

Common units for density

Here are the units you’ll see most often:

  • SI unit: kilogram per cubic meter (kg/m³).
  • Lab/chemistry unit: gram per cubic centimeter (g/cm³).
  • Liquids in chemistry: gram per milliliter (g/mL), which is numerically the same as g/cm³.
  • Engineering/older usage: kilogram per liter (kg/L), gram per liter (g/L).
  • Non-metric (especially in the U.S.): pound per cubic foot (lb/ft³), pound per cubic inch (lb/in³).

For example, water at room temperature has a density of about 1 g/cm³, which is the same as 1000 kg/m³.

If you tell me your level (middle school, high school, or college), I can tailor a quick set of practice examples using these units.