Defined as the mass of an object or substance divided by its volume (d = m/v). The standard units of density are grams/milliliters (g/mL). The density of water at 77Â°F (25Â°C) is 1.00 g/mL, which is used as a benchmark for comparison. Small amounts of dense materials (such as lead) are heavy, having a density of greater than 1.00, and they will sink when placed in water. Conversely, comparable amounts of low-density materials, such as foam, are light, have a density of less than 1.00, and will float. In forensic science, density of materials such as soil samples and glass can be used to help classify them. Density columns tubes filled with liquids of known densities are used for this purpose. These are also referred to as density gradients.