In physics, usually the density of water at the ice point (0°C), 0. 99984 g cm⁻³; or the maximum density of water (at 4°C), 0. 99997 g cm⁻³. In the U. S. Standard Atmosphere–1976, the density of air at a standard temperature of 15°C and a standard pressure of 1013. 25 mb is 1225. 00 g cm⁻³.