The temperature anomaly is multiplied by the climatological mean density of the one-degree square and the heat capacity of water and the area and volume of the one-degree square for the given standard depth. The heat contents for each volume surrounding a standard depth are summed to calculate full ocean heat content anomaly for each one degree gridbox. The values for each gridbox are summed to calculate global value. [Note this is a global integral, not an average.] The area of each one-degree gridbox is calculated similar to the attached FORTRAN subroutine (easily adaptable to any software language).