The kilogram per meter cubed (symbolized kg/m 3 ) is the standard unit of material density in the International System of Units (SI). Material density is expressed directly in base SI units, and cannot be further reduced.
A substance with a density of 1 kg/m 3 is extremely light for its size. Even styrofoam or bubble-wrap has a density greater than this. A cubic meter of water has a mass of about 1000 kg, more than a conventional English ton in the gravitational field of the earth.
Alternative units are often used to express density. The most common of these is the gram per centimeter cubed (g/cm 3 ). A substance with a density of 1 g/cm 3 has a density of 1000 kg/m 3 . Conversely, a substance with a density of 1 kg/m 3 has a density of 0.001 g/cm 3 .