The same physical quantity, such as density, can be reported using different units. You found that water has a density of 1000kg/m^3=1g/cm^3 . Because the density of water must be the same regardless of what units you use to measure it, you can conclude that an object whose density is 1 kg/m^3 must be less dense than water. In other words, 1 kg/m^3 is less than 1 g/cm^3. If you had three different objects with densities of 1 kg/m^3 , 1 g/m^3 , and 1 kg/mm^3 , which object would be the most dense?