 A cubic metre of pure water at the temperature of maximum density (3.98 °C) and standard atmospheric pressure (101.325 kPa) has a mass of , or one tonne.At 0 °C, the freezing point of water, a cubic metre of water has slightly less mass, 999.972 kilograms.It is sometimes abbreviated to cu m, m3, M3, m^3, m**3, CBM, cbm when superscript characters or markup cannot be used (e.g.