Abstract : This paper focuses on the global quantities, radius, mass, and inertia that are needed for the construction of reference Earth density models. We recall how these quantities b, M, and I are measured and we give realistic estimates and uncertainties. Since a reference model corresponds to a spherical average of the real Earth, we detail how these estimates need to be corrected in order to be used as input data for such a mean model. The main independent data to be used for reference models are: b=6 371 230±10 m, M0=(5.9733±0.0090)×10 24 kg, I0/ M0=(1.342 354±0.000 031)×10 13 m 2.