Equations are developed that can be used to determine the amount of gas present in sea ice from measurements of the bulk ice density, salinity, and temperature in the temperature range of −2 to −30 °C. Conversely these relationships can be used to give the density of sea ice as a function of its temperature and salinity, considering both the presence of gas and of solid salts in the ice. Equations are also given that allow the calculation of the gas and brine volumes in the ice at temperatures other than that at which the bulk density was determined.