Density of seawater is calculated according to the internationally accepted (UNESCO) equations. The standard error of the equation is 3.6 x 10-3 kg/m-3.
References
Millero, F.J., Poisson, A., 1981. International one-atmosphere equation of state of seawater. Deep Sea Research 28, 625-629. https://doi.org/10.1016/0198-0149(81)90122-9